NIST SP 800-61
|Course:||CS406: Information Security|
|Book:||NIST SP 800-61|
|Printed by:||Guest user|
|Date:||Thursday, November 30, 2023, 6:01 AM|
Even though information security professionals plan to effectively manage risk, incidents still occur. NIST SP 800-61 is the National Institute of Standards and Technology (NIST) special publication that gives guidelines for organizations on how to handle security incidents. Read section 2.2 on page 6 to learn more about the need for, and the benefits of, an incident response capability. Also read section 3 on pages 21-44 to learn how to appropriately handle information security incidents. Before you move on, make sure you can explain the four stages of the incident response process: preparation; detection and analysis; containment, eradication, and recovery; and post-incident activity.
Table of contents
- The Need for Incident Response
- Handling an Incident
- 1. Preparation
- 1.1. Preparing to Handle Incidents
- 1.2. Preventing Incidents
- 2. Detection and Analysis
- 2.1. Attack Vectors
- 2.2. Signs of an Incident
- 2.3. Sources of Precursors and Indicators
- 2.4. Incident Analysis
- 2.5. Incident Documentation
- 2.6. Incident Prioritization
- 2.7. Incident Notification
- 3. Containment, Eradication, and Recovery
- 3.1. Choosing a Containment Strategy
- 3.2. Evidence Gathering and Handling
- 3.3. Identifying the Attacking Hosts
- 3.4. Eradication and Recovery
- 4. Post-Incident Activity
- 4.1. Lessons Learned
- 4.2. Using Collected Incident Data
- 4.3. Evidence Retention
- 5. Incident Handling Checklist
- 6. Recommendations
The Need for Incident ResponseAttacks frequently compromise personal and business data, and it is critical to respond quickly and effectively when security breaches occur. The concept of computer security incident response has become widely accepted and implemented. One of the benefits of having an incident response capability is that it supports responding to incidents systematically (i.e., following a consistent incident handling methodology) so that the appropriate actions are taken. Incident response helps personnel to minimize loss or theft of information and disruption of services caused by incidents. Another benefit of incident response is the ability to use information gained during incident handling to better prepare for handling future incidents and to provide stronger protection for systems and data. An incident response capability also helps with dealing properly with legal issues that may arise during incidents.
Besides the business reasons to establish an incident response capability, Federal departments and agencies must comply with law, regulations, and policy directing a coordinated, effective defense against information security threats. Chief among these are the following:
- OMB's Circular No. A-130, Appendix III, released in 2000, which directs Federal agencies to "ensure that there is a capability to provide help to users when a security incident occurs in the system and to share information concerning common vulnerabilities and threats. This capability shall share information with other organizations … and should assist the agency in pursuing appropriate legal action, consistent with Department of Justice guidance".
- FISMA (from 2002), which requires agencies to have "procedures for detecting, reporting, and responding to security incidents" and establishes a centralized Federal information security incident center, in part to:
- Federal Information Processing Standards (FIPS) 200, Minimum Security Requirements for Federal Information and Information Systems , March 2006, which specifies minimum security requirements for Federal information and information systems, including incident response. The specific requirements are defined in NIST Special Publication (SP) 800–53, Recommended Security Controls for Federal Information Systems and Organizations.
- OMB Memorandum M-07-16, Safeguarding Against and Responding to the Breach of Personally Identifiable Information , May 2007, which provides guidance on reporting security incidents that involve PII.
Source: National Institute of Standards and Technology, https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-61r2.pdf
This work is published free of restrictions under the Creative Commons CC0 1.0 Universal Public Domain Dedication.
Handling an IncidentThe incident response process has several phases. The initial phase involves establishing and training an incident response team, and acquiring the necessary tools and resources. During preparation, the organization also attempts to limit the number of incidents that will occur by selecting and implementing a set of controls based on the results of risk assessments. However, residual risk will inevitably persist after controls are implemented. Detection of security breaches is thus necessary to alert the organization whenever incidents occur. In keeping with the severity of the incident, the organization can mitigate the impact of the incident by containing it and ultimately recovering from it. During this phase, activity often cycles back to detection and analysis – for example, to see if additional hosts are infected by malware while eradicating a malware incident. After the incident is adequately handled, the organization issues a report that details the cause and cost of the incident and the steps the organization should take to prevent future incidents. This section describes the major phases of the incident response process preparation, detection and analysis, containment, eradication and recovery, and post–incident activity – in detail. Figure 3–1 illustrates the incident response life cycle.
Figure 3–1. Incident Response Life Cycle
1. PreparationIncident response methodologies typically emphasize preparation – not only establishing an incident response capability so that the organization is ready to respond to incidents, but also preventing incidents by ensuring that systems, networks, and applications are sufficiently secure. Although the incident response team is not typically responsible for incident prevention, it is fundamental to the success of incident response programs. This section provides basic advice on preparing to handle incidents and on preventing incidents.
1.1. Preparing to Handle IncidentsThe lists below provide examples of tools and resources available that may be of value during incident handling. These lists are intended to be a starting point for discussions about which tools and resources an organization's incident handlers need. For example, smartphones are one way to have resilient emergency communication and coordination mechanisms. An organization should have multiple (separate and different) communication and coordination mechanisms in case of failure of one mechanism.
Incident Handler Communications and Facilities:
- Contact information for team members and others within and outside the organization (primary and backup contacts), such as law enforcement and other incident response teams; information may include phone numbers, email addresses, public encryption keys (in accordance with the encryption software described below), and instructions for verifying the contact's identity
- On-call information for other teams within the organization, including escalation information
- Incident reporting mechanisms, such as phone numbers, email addresses, online forms, and secure instant messaging systems that users can use to report suspected incidents; at least one mechanism should permit people to report incidents anonymously
- Issue tracking system for tracking incident information, status, etc.
- Smartphones to be carried by team members for off-hour support and onsite communications
- Encryption software to be used for communications among team members, within the organization and with external parties; for Federal agencies, software must use a FIPS-validated encryption algorithm
- War room for central communication and coordination; if a permanent war room is not necessary or practical, the team should create a procedure for procuring a temporary war room when needed
- Secure storage facility for securing evidence and other sensitive materials
Incident Analysis Hardware and Software:
- Digital forensic workstations and/or backup devices to create disk images, preserve log files, and save other relevant incident data
- Laptops for activities such as analyzing data, sniffing packets, and writing reports
- Spare workstations, servers, and networking equipment, or the virtualized equivalents, which may be used for many purposes, such as restoring backups and trying out malware
- Blank removable media
- Portable printer to print copies of log files and other evidence from non-networked systems
- Packet sniffers and protocol analyzers to capture and analyze network traffic
- Digital forensic software to analyze disk images
- Removable media with trusted versions of programs to be used to gather evidence from systems
- Evidence gathering accessories, including hard-bound notebooks, digital cameras, audio recorders, chain of custody forms, evidence storage bags and tags, and evidence tape, to preserve evidence for possible legal actions
Incident Analysis Resources:
- Port lists, including commonly used ports and Trojan horse ports
- Documentation for OSs, applications, protocols, and intrusion detection and antivirus products
- Network diagrams and lists of critical assets, such as database servers
- Current baselines of expected network, system, and application activity
- Cryptographic hashes of critical files to speed incident analysis, verification, and eradication
Incident Mitigation Software:
- Access to images of clean OS and application installations for restoration and recovery purposes
Each incident handler should have access to at least two computing devices (e.g., laptops). One, such as the one from the jump kit, should be used to perform packet sniffing, malware analysis, and all other actions that risk contaminating the laptop that performs them. This laptop should be scrubbed and all software reinstalled before it is used for another incident. Note that because this laptop is special purpose, it is likely to use software other than the standard enterprise tools and configurations, and whenever possible the incident handlers should be allowed to specify basic technical requirements for these special purpose investigative laptops. In addition to an investigative laptop, each incident handler should also have a standard laptop, smart phone, or other computing device for writing reports, reading email, and performing other duties unrelated to the hands-on incident analysis. Exercises involving simulated incidents can also be very useful for preparing staff for incident handling; see NIST SP 800-84 for more information on exercises and Appendix A for sample exercise scenarios.
1.2. Preventing IncidentsKeeping the number of incidents reasonably low is very important to protect the business processes of the organization. If security controls are insufficient, higher volumes of incidents may occur, overwhelming the incident response team. This can lead to slow and incomplete responses, which translate to a larger negative business impact (e.g., more extensive damage, longer periods of service and data unavailability).
It is outside the scope of this document to provide specific advice on securing networks, systems, and applications. Although incident response teams are generally not responsible for securing resources, they can be advocates of sound security practices. An incident response team may be able to identify problems that the organization is otherwise not aware of; the team can play a key role in risk assessment and training by identifying gaps. Other documents already provide advice on general security concepts and operating system and application-specific guidelines. The following text, however, provides a brief overview of some of the main recommended practices for securing networks, systems, and applications:
- Risk Assessments. Periodic risk assessments of systems and applications should determine what risks are posed by combinations of threats and vulnerabilities. This should include understanding the applicable threats, including organization-specific threats. Each risk should be prioritized, and the risks can be mitigated, transferred, or accepted until a reasonable overall level of risk is reached. Another benefit of conducting risk assessments regularly is that critical resources are identified, allowing staff to emphasize monitoring and response activities for those resources
- Host Security. All hosts should be hardened appropriately using standard configurations. In addition to keeping each host properly patched, hosts should be configured to follow the principle of least privilege – granting users only the privileges necessary for performing their authorized tasks. Hosts should have auditing enabled and should log significant security-related events. The security of hosts and their configurations should be continuously monitored. Many organizations use Security Content Automation Protocol (SCAP) expressed operating system and application configuration checklists to assist in securing hosts consistently and effectively.
- Network Security. The network perimeter should be configured to deny all activity that is not expressly permitted. This includes securing all connection points, such as virtual private networks (VPNs) and dedicated connections to other organizations
- Malware Prevention. Software to detect and stop malware should be deployed throughout the organization. Malware protection should be deployed at the host level (e.g., server and workstation operating systems), the application server level (e.g., email server, web proxies), and the application client level (e.g., email clients, instant messaging clients).
- User Awareness and Training. Users should be made aware of policies and procedures regarding appropriate use of networks, systems, and applications. Applicable lessons learned from previous incidents should also be shared with users so they can see how their actions could affect the organization. Improving user awareness regarding incidents should reduce the frequency of incidents. IT staff should be trained so that they can maintain their networks, systems, and applications in accordance with the organization's security standard
2. Detection and Analysis
Figure 3–2. Incident Response Life Cycle (Detection and Analysis)
2.1. Attack VectorsIncidents can occur in countless ways, so it is infeasible to develop step-by-step instructions for handling every incident. Organizations should be generally prepared to handle any incident but should focus on being prepared to handle incidents that use common attack vectors. Different types of incidents merit different response strategies. The attack vectors listed below are not intended to provide definitive classification for incidents; rather, they simply list common methods of attack, which can be used as a basis for defining more specific handling procedures.
- External/Removable Media: An attack executed from removable media or a peripheral device – for example, malicious code spreading onto a system from an infected USB flash drive
- Attrition: An attack that employs brute force methods to compromise, degrade, or destroy systems, networks, or services (e.g., a DDoS intended to impair or deny access to a service or application; a brute force attack against an authentication mechanism, such as passwords, CAPTCHAS, or digital signatures).
- Web: An attack executed from a website or web-based application – for example, a cross-site scripting attack used to steal credentials or a redirect to a site that exploits a browser vulnerability and installs malware.
- Email: An attack executed via an email message or attachment – for example, exploit code disguised as an attached document or a link to a malicious website in the body of an email message.
- Impersonation: An attack involving replacement of something benign with something malicious – for example, spoofing, man in the middle attacks, rogue wireless access points, and SQL injection attacks all involve impersonation.
- Improper Usage: Any incident resulting from violation of an organization's acceptable usage policies by an authorized user, excluding the above categories; for example, a user installs file sharing software, leading to the loss of sensitive data; or a user performs illegal activities on a system.
- Loss or Theft of Equipment: The loss or theft of a computing device or media used by the organization, such as a laptop, smartphone, or authentication token.
- Other: An attack that does not fit into any of the other categories.
2.2. Signs of an IncidentFor many organizations, the most challenging part of the incident response process is accurately detecting and assessing possible incidents – determining whether an incident has occurred and, if so, the type, extent, and magnitude of the problem. What makes this so challenging is a combination of three factors:
- Incidents may be detected through many different means, with varying levels of detail and fidelity. Automated detection capabilities include network-based and host-based IDPSs, antivirus software, and log analyzers. Incidents may also be detected through manual means, such as problems reported by users. Some incidents have overt signs that can be easily detected, whereas others are almost impossible to detect
- The volume of potential signs of incidents is typically high – for example, it is not uncommon for an organization to receive thousands or even millions of intrusion detection sensor alerts per day. (See Section 3.2.4 for information on analyzing such alerts.)
- Deep, specialized technical knowledge and extensive experience are necessary for proper and efficient analysis of incident–related data.
Signs of an incident fall into one of two categories: precursors and indicators. A precursor is a sign that an incident may occur in the future. An indicator is a sign that an incident may have occurred or may be occurring now.
Most attacks do not have any identifiable or detectable precursors from the target's perspective. If precursors are detected, the organization may have an opportunity to prevent the incident by altering its security posture to save a target from attack. At a minimum, the organization could monitor activity involving the target more closely. Examples of precursors are:
- Web server log entries that show the usage of a vulnerability scanner
- An announcement of a new exploit that targets a vulnerability of the organization's mail server
- A threat from a group stating that the group will attack the organization.
While precursors are relatively rare, indicators are all too common. Too many types of indicators exist to exhaustively list them, but some examples are listed below:
- A network intrusion detection sensor alerts when a buffer overflow attempt occurs against a database server.
- Antivirus software alerts when it detects that a host is infected with malware
- A system administrator sees a filename with unusual characters
- A host records an auditing configuration change in its log.
- An application logs multiple failed login attempts from an unfamiliar remote system.
- An email administrator sees a large number of bounced emails with suspicious content.
- A network administrator notices an unusual deviation from typical network traffic flows.
2.3. Sources of Precursors and IndicatorsPrecursors and indicators are identified using many different sources, with the most common being computer security software alerts, logs, publicly available information, and people. Table 3-2 lists common sources of precursors and indicators for each category.
Table 3–1. Common Sources of Precursors and Indicators
|IDPSs||IDPS products identify suspicious events and record pertinent data regarding them, including the date and time the attack was detected, the type of attack, the source and destination IP addresses, and the username (if applicable and known). Most IDPS products use attack signatures to identify malicious activity; the signatures must be kept up to date so that the newest attacks can be detected. IDPS software often produces false positive – alerts that indicate malicious activity is occurring, when in fact there has been none. Analysts should manually validate IDPS alerts either by closely reviewing the recorded supporting data or by getting related data from other sources.|
|SIEMs||Security Information and Event Management (SIEM) products are similar to IDPS products, but they generate alerts based on analysis of log data (see below)|
|Antivirus and antispam software||Antivirus software detects various forms of malware, generates alerts, and prevents the malware from infecting hosts. Current antivirus products are effective at stopping many instances of malware if their signatures are kept up to date. Antispam software is used to detect spam and prevent it from reaching users' mailboxes. Spam may contain malware, phishing attacks, and other malicious content, so alerts from antispam software may indicate attack attempts.|
|File integrity checking software||File integrity checking software can detect changes made to important files during incidents. It uses a hashing algorithm to obtain a cryptographic checksum for each designated file. If the file is altered and the checksum is recalculated, an extremely high probability exists that the new checksum will not match the old checksum. By regularly recalculating checksums and comparing them with previous values, changes to files can be detected.|
|Third – party monitoring services||Third parties offer a variety of subscription-based and free monitoring services. An example is fraud detection services that will notify an organization if its IP addresses, domain names, etc. are associated with current incident activity involving other organizations. There are also free real-time blacklists with similar information. Another example of a third-party monitoring service is a CSIRC notification list; these lists are often available only to other incident response teams.|
|Operating system, service and application logs||Logs from operating systems, services, and applications (particularly audit-related data) are frequently of great value when an incident occurs, such as recording which accounts were accessed and what actions were performed. Organizations should require a baseline level of logging on all systems and a higher baseline level on critical systems. Logs can be used for analysis by correlating event information. Depending on the event information, an alert can be generated to indicate an incident. Section 3.2.4 discusses the value of centralized logging.|
|Network device logs||Logs from network devices such as firewalls and routers are not typically a primary source of precursors or indicators. Although these devices are usually configured to log blocked connection attempts, they provide little information about the nature of the activity. Still, they can be valuable in identifying network trends and in correlating events detected by other devices.|
|Network flows||A network flow is a particular communication session occurring between hosts. Routers and other networking devices can provide network flow information, which can be used to find anomalous network activity caused by malware, data exfiltration, and other malicious acts. There are many standards for flow data formats, including NetFlow, sFlow, and IPFIX.|
|Publicly Available Information|
|Information on new vulnerabilities and exploits||Keeping up with new vulnerabilities and exploits can prevent some incidents from occurring and assist in detecting and analyzing new attacks. The National Vulnerability Database (NVD) contains information on vulnerabilities. Organizations such as US–CERT33 and CERT® /CC periodically provide threat update information through briefings, web postings, and mailing lists.|
|People from within the organization||Users, system administrators, network administrators, security staff, and others from within the organization may report signs of incidents. It is important to validate all such reports. One approach is to ask people who provide such information how confident they are of the accuracy of the information. Recording this estimate along with the information provided can help considerably during incident analysis, particularly when conflicting data is discovered.|
|People from other organizations||Reports of incidents that originate externally should be taken seriously. For example, the organization might be contacted by a party claiming a system at the organization is attacking its systems. External users may also report other indicators, such as a defaced web page or an unavailable service. Other incident response teams also may report incidents. It is important to have mechanisms in place for external parties to report indicators and for trained staff to monitor those mechanisms carefully; this may be as simple as setting up a phone number and email address, configured to forward messages to the help desk.|
2.4. Incident Analysis
Incident detection and analysis would be easy if every precursor or indicator were guaranteed to be accurate; unfortunately, this is not the case. For example, user-provided indicators such as a complaint of a server being unavailable are often incorrect.
Intrusion detection systems may produce false positives – incorrect indicators. These examples demonstrate what makes incident detection and analysis so difficult: each indicator ideally should be evaluated to determine if it is legitimate. Making matters worse, the total number of indicators may be thousands or millions a day. Finding the real security incidents that occurred out of all the indicators can be a daunting task. Even if an indicator is accurate, it does not necessarily mean that an incident has occurred. Some indicators, such as a server crash or modification of critical files, could happen for several reasons other than a security incident, including human error. Given the occurrence of indicators, however, it is reasonable to suspect that an incident might be occurring and to act accordingly. Determining whether a particular event is actually an incident is sometimes a matter of judgment. It may be necessary to collaborate with other technical and information security personnel to make a decision. In many instances, a situation should be handled the same way regardless of whether it is security related. For example, if an organization is losing Internet connectivity every 12 hours and no one knows the cause, the staff would want to resolve the problem just as quickly and would use the same resources to diagnose the problem, regardless of its cause.
Some incidents are easy to detect, such as an obviously defaced web page. However, many incidents are not associated with such clear symptoms. Small signs such as one change in one system configuration file may be the only indicators that an incident has occurred. In incident handling, detection may be the most difficult task. Incident handlers are responsible for analyzing ambiguous, contradictory, and incomplete symptoms to determine what has happened. Although technical solutions exist that can make detection easier, the best remedy is to build a team of highly experienced and proficient staff members who can analyze the precursors and indicators effectively and efficiently and take appropriate actions. Without a well-trained and capable staff, incident detection and analysis will be conducted inefficiently, and costly mistakes will be made.
The incident response team should work quickly to analyze and validate each incident, following a predefined process and documenting each step taken. When the team believes that an incident has occurred, the team should rapidly perform an initial analysis to determine the incident’s scope, such as which networks, systems, or applications are affected; who or what originated the incident; and how the incident is occurring (e.g., what tools or attack methods are being used, what vulnerabilities are being exploited). The initial analysis should provide enough information for the team to prioritize subsequent activities, such as containment of the incident and deeper analysis of the effects of the incident.
Performing the initial analysis and validation is challenging. The following are recommendations for
making incident analysis easier and more effective:
- Profile Networks and Systems. Profiling is measuring the characteristics of expected activity so that
changes to it can be more easily identified. Examples of profiling are running file integrity checking
software on hosts to derive checksums for critical files and monitoring network bandwidth usage to
determine what the average and peak usage levels are on various days and times. In practice, it is
difficult to detect incidents accurately using most profiling techniques; organizations should use
profiling as one of several detection and analysis techniques.
- Understand Normal Behaviors. Incident response team members should study networks, systems,
and applications to understand what their normal behavior is so that abnormal behavior can be
recognized more easily. No incident handler will have a comprehensive knowledge of all behavior
throughout the environment, but handlers should know which experts could fill in the gaps. One way
to gain this knowledge is through reviewing log entries and security alerts. This may be tedious if
filtering is not used to condense the logs to a reasonable size. As handlers become more familiar with
the logs and alerts, they should be able to focus on unexplained entries, which are usually more
important to investigate. Conducting frequent log reviews should keep the knowledge fresh, and the
analyst should be able to notice trends and changes over time. The reviews also give the analyst an
indication of the reliability of each source.
- Create a Log Retention Policy. Information regarding an incident may be recorded in several places,
such as firewall, IDPS, and application logs. Creating and implementing a log retention policy that
specifies how long log data should be maintained may be extremely helpful in analysis because older
log entries may show reconnaissance activity or previous instances of similar attacks. Another reason
for retaining logs is that incidents may not be discovered until days, weeks, or even months later. The
length of time to maintain log data is dependent on several factors, including the organization’s data
retention policies and the volume of data. See NIST SP 800-92, Guide to Computer Security Log
Management for additional recommendations related to logging.
- Perform Event Correlation. Evidence of an incident may be captured in several logs that each
contain different types of data – a firewall log may have the source IP address that was used, whereas
an application log may contain a username. A network IDPS may detect that an attack was launched
against a particular host, but it may not know if the attack was successful. The analyst may need to
examine the host’s logs to determine that information. Correlating events among multiple indicator
sources can be invaluable in validating whether a particular incident occurred.
- Keep All Host Clocks Synchronized. Protocols such as the Network Time Protocol (NTP)
synchronize clocks among hosts. Event correlation will be more complicated if the devices reporting
events have inconsistent clock settings. From an evidentiary standpoint, it is preferable to have
consistent timestamps in logs – for example, to have three logs that show an attack occurred at
12:07:01 a.m., rather than logs that list the attack as occurring at 12:07:01, 12:10:35, and 11:07:06.
- Maintain and Use a Knowledge Base of Information. The knowledge base should include
information that handlers need for referencing quickly during incident analysis. Although it is
possible to build a knowledge base with a complex structure, a simple approach can be effective. Text
documents, spreadsheets, and relatively simple databases provide effective, flexible, and searchable
mechanisms for sharing data among team members. The knowledge base should also contain a
variety of information, including explanations of the significance and validity of precursors and
indicators, such as IDPS alerts, operating system log entries, and application error codes.
- Use Internet Search Engines for Research. Internet search engines can help analysts find
information on unusual activity. For example, an analyst may see some unusual connection attempts
targeting TCP port 22912. Performing a search on the terms "TCP," "port," and "22912" may return
some hits that contain logs of similar activity or even an explanation of the significance of the port
number. Note that separate workstations should be used for research to minimize the risk to the
organization from conducting these searches.
- Run Packet Sniffers to Collect Additional Data. Sometimes the indicators do not record enough
detail to permit the handler to understand what is occurring. If an incident is occurring over a
network, the fastest way to collect the necessary data may be to have a packet sniffer capture network
traffic. Configuring the sniffer to record traffic that matches specified criteria should keep the volume
of data manageable and minimize the inadvertent capture of other information. Because of privacy
concerns, some organizations may require incident handlers to request and receive permission before
using packet sniffers.
- Filter the Data. There is simply not enough time to review and analyze all the indicators; at
minimum the most suspicious activity should be investigated. One effective strategy is to filter out
categories of indicators that tend to be insignificant. Another filtering strategy is to show only the
categories of indicators that are of the highest significance; however, this approach carries substantial
risk because new malicious activity may not fall into one of the chosen indicator categories.
- Seek Assistance from Others. Occasionally, the team will be unable to determine the full cause and nature of an incident. If the team lacks sufficient information to contain and eradicate the incident, then it should consult with internal resources (e.g., information security staff) and external resources (e.g., US-CERT, other CSIRTs, contractors with incident response expertise). It is important to accurately determine the cause of each incident so that it can be fully contained and the exploited vulnerabilities can be mitigated to prevent similar incidents from occurring.
2.5. Incident Documentation
An incident response team that suspects that an incident has occurred should immediately start recording all facts regarding the incident. A logbook is an effective and simple medium for this, but laptops, audio recorders, and digital cameras can also serve this purpose. Documenting system events, conversations, and observed changes in files can lead to a more efficient, more systematic, and less errorprone handling of the problem. Every step taken from the time the incident was detected to its final resolution should be documented and timestamped. Every document regarding the incident should be dated and signed by the incident handler. Information of this nature can also be used as evidence in a court of law if legal prosecution is pursued. Whenever possible, handlers should work in teams of at least two: one person can record and log events while the other person performs the technical tasks. Section 3.3.2 presents more information about evidence.
The incident response team should maintain records about the status of incidents, along with other
pertinent information. Using an application or a database, such as an issue tracking system, helps ensure
that incidents are handled and resolved in a timely manner. The issue tracking system should contain
information on the following:
The current status of the incident (new, in progress, forwarded for investigation, resolved, etc.)
- A summary of the incident
- Indicators related to the incident
- Other incidents related to this incident
- Actions taken by all incident handlers on this incident
- Chain of custody, if applicable
- Impact assessments related to the incident
- Contact information for other involved parties (e.g., system owners, system administrators)
- A list of evidence gathered during the incident investigation
- Comments from incident handlers
- Next steps to be taken (e.g., rebuild the host, upgrade an application).
The incident response team should safeguard incident data and restrict access to it because it often
contains sensitive information – for example, data on exploited vulnerabilities, recent security breaches,
and users that may have performed inappropriate actions. For example, only authorized personnel should
have access to the incident database. Incident communications (e.g., emails) and documents should be
encrypted or otherwise protected so that only authorized personnel can read them.
2.6. Incident Prioritization
Prioritizing the handling of the incident is perhaps the most critical decision point in the incident handling process. Incidents should not be handled on a first-come, first-served basis as a result of resource limitations. Instead, handling should be
prioritized based on the relevant factors, such as the following:
- Functional Impact of the Incident. Incidents targeting IT systems typically impact the business functionality that those systems provide, resulting in some type of negative impact to the users of those systems. Incident handlers should
consider how the incident will impact the existing functionality of the affected systems. Incident handlers should consider not only the current functional impact of the incident, but also the likely future functional impact of the incident if
it is not immediately contained.
- Information Impact of the Incident. Incidents may affect the confidentiality, integrity, and availability of the organization's information. For example, a malicious agent may exfiltrate sensitive information. Incident handlers should
consider how this information exfiltration will impact the organization's overall mission. An incident that results in the exfiltration of sensitive information may also affect other organizations if any of the data pertained to a partner organization.
- Recoverability from the Incident. The size of the incident and the type of resources it affects will determine the amount of time and resources that must be spent on recovering from that incident. In some instances it is not possible to recover from an incident (e.g., if the confidentiality of sensitive information has been compromised) and it would not make sense to spend limited resources on an elongated incident handling cycle, unless that effort was directed at ensuring that a similar incident did not occur in the future. In other cases, an incident may require far more resources to handle than what an organization has available. Incident handlers should consider the effort necessary to actually recover from an incident and carefully weigh that against the value the recovery effort will create and any requirements related to incident handling.
Combining the functional impact to the organization's systems and the impact to the organization's information determines the business impact of the incident – for example, a distributed denial of service attack against a public web server may temporarily
reduce the functionality for users attempting to access the server, whereas unauthorized root-level access to a public web server may result in the exfiltration of personally identifiable information (PII), which could have a long-lasting impact on
the organization's reputation.
The recoverability from the incident determines the possible responses that the team may take when handling the incident. An incident with a high functional impact and low effort to recover from is an ideal candidate for immediate action from the team.
However, some incidents may not have smooth recovery paths and may need to be queued for a more strategic-level response – for example, an incident that results in an attacker exfiltrating and publicly posting gigabytes of sensitive data has no easy
recovery path since the data is already exposed; in this case the team may transfer part of the responsibility for handling the data exfiltration incident to a more strategic-level team that develops strategy for preventing future breaches and creates
an outreach plan for alerting those individuals or organizations whose data was exfiltrated. The team should prioritize the response to each incident based on its estimate of the business impact caused by the incident and the estimated efforts required
to recover from the incident.
An organization can best quantify the effect of its own incidents because of its situational awareness. Table 3-2 provides examples of functional impact categories that an organization might use for rating its own incidents. Rating incidents can be helpful
in prioritizing limited resources.
Table 3-2. Functional Impact Categories
|None||No effect to the organization's ability to provide all services to all users|
|Low||Minimal effect; the organization can still provide all critical services to all users but has lost efficiency|
|Medium||Organization has lost the ability to provide a critical service to a subset of system users|
|High||Organization is no longer able to provide some critical services to any users|
Table 3-3. Information Impact Categories
|None||No information was exfiltrated, changed, deleted, or otherwise compromised|
|Privacy Breach||Sensitive personally identifiable information (PII) of taxpayers, employees, beneficiaries, etc. was accessed or exfiltrated|
|Proprietary Breach||Unclassified proprietary information, such as protected critical infrastructure information (PCII), was accessed or exfiltrated|
|Integrity Loss||Sensitive or proprietary information was changed or deleted|
Table 3-4. Recoverability Effort Categories
|Regular||Time to recovery is predictable with existing resources|
|Supplemented||Time to recovery is predictable with additional resources|
|Extended||Time to recovery is unpredictable; additional resources and outside help are needed|
|Not Recoverable||Recovery from the incident is not possible (e.g., sensitive data exfiltrated and posted publicly); launch investigation|
2.7. Incident Notification
When an incident is analyzed and prioritized, the incident response team needs to notify the appropriate
individuals so that all who need to be involved will play their roles. Incident response policies should include provisions concerning incident reporting – at a minimum, what must be reported to whom and at
what times (e.g., initial notification, regular status updates). The exact reporting requirements vary among
organizations, but parties that are typically notified include:
- Head of information security
- Local information security officer
- Other incident response teams within the organization
- External incident response teams (if appropriate)
- System owner
- Human resources (for cases involving employees, such as harassment through email)
- Public affairs (for incidents that may generate publicity)
- Legal department (for incidents with potential legal ramifications)
- US–CERT (required for Federal agencies and systems operated on behalf of the Federal government; see Section 220.127.116.11)
- Law enforcement (if appropriate)
During incident handling, the team may need to provide status updates to certain parties, even in some
cases the entire organization. The team should plan and prepare several communication methods,
including out-of-band methods (e.g., in person, paper), and select the methods that are appropriate for a
particular incident. Possible communication methods include:
- Website (internal, external, or portal)
- Telephone calls
- In person (e.g., daily briefings)
- Voice mailbox greeting (e.g., set up a separate voice mailbox for incident updates, and update the greeting message to reflect the current incident status; use the help desk's voice mail greeting)
- Paper (e.g., post notices on bulletin boards and doors, hand out notices at all entrance points).
3. Containment, Eradication, and Recovery
Figure 3-3. Incident Response Life Cycle (Containment, Eradication, and Recovery)
3.1. Choosing a Containment Strategy
Containment is important before an incident overwhelms resources or increases damage. Most incidents
require containment, so that is an important consideration early in the course of handling each incident.
Containment provides time for developing a tailored remediation strategy. An essential part of
containment is decision-making (e.g., shut down a system, disconnect it from a network, disable certain
functions). Such decisions are much easier to make if there are predetermined strategies and procedures
for containing the incident. Organizations should define acceptable risks in dealing with incidents and
develop strategies accordingly.
Containment strategies vary based on the type of incident. For example, the strategy for containing an
email-borne malware infection is quite different from that of a network-based DDoS attack. Organizations
should create separate containment strategies for each major incident type, with criteria documented
clearly to facilitate decision-making. Criteria for determining the appropriate strategy include:
- Potential damage to and theft of resources
- Need for evidence preservation
- Service availability (e.g., network connectivity, services provided to external parties)
- Time and resources needed to implement the strategy
- Effectiveness of the strategy (e.g., partial containment, full containment)
- Duration of the solution (e.g., emergency workaround to be removed in four hours, temporary workaround to be removed in two weeks, permanent solution).
In certain cases, some organizations redirect the attacker to a sandbox (a form of containment) so that
they can monitor the attacker's activity, usually to gather additional evidence. The incident response team
should discuss this strategy with its legal department to determine if it is feasible. Ways of monitoring an attacker's activity other than sandboxing should not be used; if an organization knows that a system has
been compromised and allows the compromise to continue, it may be liable if the attacker uses the
compromised system to attack other systems. The delayed containment strategy is dangerous because an
attacker could escalate unauthorized access or compromise other systems.
Another potential issue regarding containment is that some attacks may cause additional damage when
they are contained. For example, a compromised host may run a malicious process that pings another host
periodically. When the incident handler attempts to contain the incident by disconnecting the
compromised host from the network, the subsequent pings will fail. As a result of the failure, the
malicious process may overwrite or encrypt all the data on the host's hard drive. Handlers should not
assume that just because a host has been disconnected from the network, further damage to the host has
3.2. Evidence Gathering and Handling
Although the primary reason for gathering evidence during an incident is to resolve the incident, it may
also be needed for legal proceedings. In such cases, it is important to clearly document how all
evidence, including compromised systems, has been preserved. Evidence should be collected according
to procedures that meet all applicable laws and regulations that have been developed from previous
discussions with legal staff and appropriate law enforcement agencies so that any evidence can be
admissible in court. In addition, evidence should be accounted for at all times; whenever evidence is
transferred from person to person, chain of custody forms should detail the transfer and include each
party's signature. A detailed log should be kept for all evidence, including the following:
- Identifying information (e.g., the location, serial number, model number, hostname, media access control (MAC) addresses, and IP addresses of a computer)
- Name, title, and phone number of each individual who collected or handled the evidence during the investigation
- Time and date (including time zone) of each occurrence of evidence handling
- Locations where the evidence was stored.
Collecting evidence from computing resources presents some challenges. It is generally desirable to
acquire evidence from a system of interest as soon as one suspects that an incident may have occurred.
Many incidents cause a dynamic chain of events to occur; an initial system snapshot may do more good in
identifying the problem and its source than most other actions that can be taken at this stage. From an
evidentiary standpoint, it is much better to get a snapshot of the system as-is rather than doing so after
incident handlers, system administrators, and others have inadvertently altered the state of the machine
during the investigation. Users and system administrators should be made aware of the steps that they
should take to preserve evidence. See NIST SP 800-86, Guide to Integrating Forensic Techniques into
Incident Response, for additional information on preserving evidence.
3.3. Identifying the Attacking Hosts
During incident handling, system owners and others sometimes want to or need to identify the attacking
host or hosts. Although this information can be important, incident handlers should generally stay focused
on containment, eradication, and recovery. Identifying an attacking host can be a time-consuming and
futile process that can prevent a team from achieving its primary goal – minimizing the business impact.
The following items describe the most commonly performed activities for attacking host identification:
- Validating the Attacking Host's IP Address. New incident handlers often focus on the attacking
host's IP address. The handler may attempt to validate that the address was not spoofed by verifying
connectivity to it; however, this simply indicates that a host at that address does or does not respond
to the requests. A failure to respond does not mean the address is not real – for example, a host may
be configured to ignore pings and traceroutes. Also, the attacker may have received a dynamic
address that has already been reassigned to someone else.
- Researching the Attacking Host through Search Engines. Performing an Internet search using the
apparent source IP address of an attack may lead to more information on the attack – for example, a
mailing list message regarding a similar attack.
- Using Incident Databases. Several groups collect and consolidate incident data from various
organizations into incident databases. This information sharing may take place in many forms, such
as trackers and real-time blacklists. The organization can also check its own knowledge base or issue
tracking system for related activity.
- Monitoring Possible Attacker Communication Channels. Incident handlers can monitor communication channels that may be used by an attacking host. For example, many bots use IRC as their primary means of communication. Also, attackers may congregate on certain IRC channels to brag about their compromises and share information. However, incident handlers should treat any such information that they acquire only as a potential lead, not as fact.
3.4. Eradication and Recovery
After an incident has been contained, eradication may be necessary to eliminate components of the
incident, such as deleting malware and disabling breached user accounts, as well as identifying and
mitigating all vulnerabilities that were exploited. During eradication, it is important to identify all affected
hosts within the organization so that they can be remediated. For some incidents, eradication is either not
necessary or is performed during recovery.
In recovery, administrators restore systems to normal operation, confirm that the systems are functioning
normally, and (if applicable) remediate vulnerabilities to prevent similar incidents. Recovery may involve
such actions as restoring systems from clean backups, rebuilding systems from scratch, replacing
compromised files with clean versions, installing patches, changing passwords, and tightening network
perimeter security (e.g., firewall rulesets, boundary router access control lists). Higher levels of system
logging or network monitoring are often part of the recovery process. Once a resource is successfully
attacked, it is often attacked again, or other resources within the organization are attacked in a similar
Eradication and recovery should be done in a phased approach so that remediation steps are prioritized.
For large-scale incidents, recovery may take months; the intent of the early phases should be to increase
the overall security with relatively quick (days to weeks) high value changes to prevent future incidents.
The later phases should focus on longer-term changes (e.g., infrastructure changes) and ongoing work to
keep the enterprise as secure as possible.
Because eradication and recovery actions are typically OS or application – specific, detailed
recommendations and advice regarding them are outside the scope of this document.
4. Post-Incident Activity
Figure 3-4. Incident Response Life Cycle (Post-Incident Activity)
4.1. Lessons Learned
One of the most important parts of incident response is also the most often omitted: learning and
improving. Each incident response team should evolve to reflect new threats, improved technology, and
lessons learned. Holding a "lessons learned" meeting with all involved parties after a major incident, and
optionally periodically after lesser incidents as resources permit, can be extremely helpful in improving
security measures and the incident handling process itself. Multiple incidents can be covered in a single
lessons learned meeting. This meeting provides a chance to achieve closure with respect to an incident by
reviewing what occurred, what was done to intervene, and how well intervention worked. The meeting
should be held within several days of the end of the incident. Questions to be answered in the meeting
- Exactly what happened, and at what times?
- How well did staff and management perform in dealing with the incident? Were the documented procedures followed? Were they adequate?
- What information was needed sooner?
- Were any steps or actions taken that might have inhibited the recovery?
- What would the staff and management do differently the next time a similar incident occurs?
- How could information sharing with other organizations have been improved?
- What corrective actions can prevent similar incidents in the future?
- What precursors or indicators should be watched for in the future to detect similar incidents?
- What additional tools or resources are needed to detect, analyze, and mitigate future incidents?
Small incidents need limited post-incident analysis, with the exception of incidents performed through
new attack methods that are of widespread concern and interest. After serious attacks have occurred, it is
usually worthwhile to hold post-mortem meetings that cross team and organizational boundaries to
provide a mechanism for information sharing. The primary consideration in holding such meetings is
ensuring that the right people are involved. Not only is it important to invite people who have been
involved in the incident that is being analyzed, but also it is wise to consider who should be invited for the
purpose of facilitating future cooperation.
The success of such meetings also depends on the agenda. Collecting input about expectations and needs
(including suggested topics to cover) from participants before the meeting increases the likelihood that the
participants' needs will be met. In addition, establishing rules of order before or during the start of a
meeting can minimize confusion and discord. Having one or more moderators who are skilled in group
facilitation can yield a high payoff. Finally, it is also important to document the major points of
agreement and action items and to communicate them to parties who could not attend the meeting.
Lessons learned meetings provide other benefits. Reports from these meetings are good material for
training new team members by showing them how more experienced team members respond to incidents.
Updating incident response policies and procedures is another important part of the lessons learned
process. Post-mortem analysis of the way an incident was handled will often reveal a missing step or an
inaccuracy in a procedure, providing impetus for change. Because of the changing nature of information
technology and changes in personnel, the incident response team should review all related documentation
and procedures for handling incidents at designated intervals.
Another important post-incident activity is creating a follow-up report for each incident, which can be
quite valuable for future use. The report provides a reference that can be used to assist in handling similar
incidents. Creating a formal chronology of events (including timestamped information such as log data
from systems) is important for legal reasons, as is creating a monetary estimate of the amount of damage
the incident caused. This estimate may become the basis for subsequent prosecution activity by entities
such as the U.S. Attorney General's office. Follow-up reports should be kept for a period of time as
specified in record retention policies.
4.2. Using Collected Incident Data
Lessons learned activities should produce a set of objective and subjective data regarding each incident. Over time, the collected incident data should be useful in several capacities. The data, particularly the total hours of involvement and the cost,
may be used to justify additional funding of the incident response team. A study of incident characteristics may indicate systemic security weaknesses and threats, as well as changes in incident trends. This data can be put back into the risk assessment
process, ultimately leading to the selection and implementation of additional controls. Another good use of the data is measuring the success of the incident response team. If incident data is collected and stored properly, it should provide several
measures of the success (or at least the activities) of the incident response team. Incident data can also be collected to determine if a change to incident response capabilities causes a corresponding change in the team's performance (e.g., improvements
in efficiency, reductions in costs). Furthermore, organizations that are required to report incident information will need to collect the necessary data to meet their requirements. See Section 4 for additional information on sharing incident
data with other organizations.
Organizations should focus on collecting data that is actionable, rather than collecting data simply because it is available. For example, counting the number of precursor port scans that occur each week and producing a chart at the end of the year that
shows port scans increased by eight percent is not very helpful and may be quite time-consuming. Absolute numbers are not informative – understanding how they represent threats to the business processes of the organization is what matters. Organizations
should decide what incident data to collect based on reporting requirements and on the expected return on investment from the data (e.g., identifying a new threat and mitigating the related vulnerabilities before they can be exploited.) Possible metrics
for incident-related data include:
- Number of Incidents Handled. Handling more incidents is not necessarily better – for example, the number of incidents handled may decrease because of better network and host security controls, not because of negligence by the incident
response team. The number of incidents handled is best taken as a measure of the relative amount of work that the incident response team had to perform, not as a measure of the quality of the team, unless it is considered in the context of other
measures that collectively give an indication of work quality. It is more effective to produce separate incident counts for each incident category. Subcategories also can be used to provide more information. For example, a growing number of incidents
performed by insiders could prompt stronger policy provisions concerning background investigations for personnel and misuse of computing resources and stronger security controls on internal networks (e.g., deploying intrusion detection software
to more internal networks and hosts).
- Time Per Incident. For each incident, time can be measured in several ways:
– Total amount of labor spent working on the incident
– Elapsed time from the beginning of the incident to incident discovery, to the initial impact assessment, and to each stage of the incident handling process (e.g., containment, recovery)
– How long it took the incident response team to respond to the initial report of the incident
– How long it took to report the incident to management and, if necessary, appropriate external entities (e.g., US-CERT).
- Objective Assessment of Each Incident. The response to an incident that has been resolved can be analyzed to determine how effective it was. The following are examples of performing an objective assessment of an incident:
– Reviewing logs, forms, reports, and other incident documentation for adherence to established incident response policies and procedures
– Identifying which precursors and indicators of the incident were recorded to determine how effectively the incident was logged and identified
– Determining if the incident caused damage before it was detected
– Determining if the actual cause of the incident was identified, and identifying the vector of attack, the vulnerabilities exploited, and the characteristics of the targeted or victimized systems, networks, and applications
– Determining if the incident is a recurrence of a previous incident
– Calculating the estimated monetary damage from the incident (e.g., information and critical business processes negatively affected by the incident)
– Measuring the difference between the initial impact assessment and the final impact assessment (see Section 3.2.6)
– Identifying which measures, if any, could have prevented the incident.
- Subjective Assessment of Each Incident. Incident response team members may be asked to assess their own performance, as well as that of other team members and of the entire team. Another valuable source of input is the owner of a resource that was attacked, in order to determine if the owner thinks the incident was handled efficiently and if the outcome was satisfactory.
Incident response policies, plans, and procedures
Tools and resources
Team model and structure
Incident handler training and education
Incident documentation and reports
The measures of success discussed earlier in this section
4.3. Evidence Retention
Organizations should establish policy for how long evidence from an incident should be retained. Most
organizations choose to retain all evidence for months or years after the incident ends. The following
factors should be considered during the policy creation:
- Prosecution. If it is possible that the attacker will be prosecuted, evidence may need to be retained
until all legal actions have been completed. In some cases, this may take several years. Furthermore,
evidence that seems insignificant now may become more important in the future. For example, if an
attacker is able to use knowledge gathered in one attack to perform a more severe attack later,
evidence from the first attack may be key to explaining how the second attack was accomplished.
- Data Retention. Most organizations have data retention policies that state how long certain types of
data may be kept. For example, an organization may state that email messages should be retained for
only 180 days. If a disk image contains thousands of emails, the organization may not want the image
to be kept for more than 180 days unless it is absolutely necessary. As discussed in Section 3.4.2,
General Records Schedule (GRS) 24 specifies that incident handling records should be kept for
- Cost. Original hardware (e.g., hard drives, compromised systems) that is stored as evidence, as well as hard drives and removable media that are used to hold disk images, are generally individually inexpensive. However, if an organization stores many such components for years, the cost can be substantial. The organization also must retain functional computers that can use the stored hardware and media.
5. Incident Handling Checklist
The checklist in Table 3-5 provides the major steps to be performed in the handling of an incident. Note that the actual steps performed may vary based on the type of incident and the nature of individual incidents. For example, if the handler knows exactly
what has happened based on analysis of indicators (Step 1.1), there may be no need to perform Steps 1.2 or 1.3 to further research the activity. The checklist provides guidelines to handlers on the major steps that should be performed; it does not
dictate the exact sequence of steps that should always be followed.
Table 3-5. Incident Handling Checklist
|Detection and Analysis|
|1.||Determine whether an incident has occurred|
Analyze the precursors and indicators
Look for correlating information
Perform research (e.g., search engines, knowledge base)
As soon as the handler believes an incident has occurred, begin documenting the investigation and gathering evidence
|2.||Prioritize handling the incident based on the relevant factors (functional impact, information impact, recoverability effort, etc.)|
|3.||Report the incident to the appropriate internal personnel and external organizations|
|Containment, Eradication, and Recovery|
|4.||Acquire, preserve, secure, and document evidence|
|5.||Contain the incident|
|6.||Eradicate the incident|
Identify and mitigate all vulnerabilities that were exploited
Remove malware, inappropriate materials, and other components
If more affected hosts are discovered (e.g., new malware infections), repeat the Detection and Analysis steps (1.1, 1.2) to identify all other affected hosts, then contain (5) and eradicate (6) the incident for them
|7.||Recover from the incident|
Return affected systems to an operationally ready state
Confirm that the affected systems are functioning normally
If necessary, implement additional monitoring to look for future related activity
|8.||Create a follow-up report|
|9.||Hold a lessons learned meeting (mandatory for major incidents, optional otherwise)|
- Acquire tools and resources that may be of value during incident handling. The team will be
more efficient at handling incidents if various tools and resources are already available to them.
Examples include contact lists, encryption software, network diagrams, backup devices, digital
forensic software, and port lists.
- Prevent incidents from occurring by ensuring that networks, systems, and applications are
sufficiently secure. Preventing incidents is beneficial to the organization and also reduces the
workload of the incident response team. Performing periodic risk assessments and reducing the
identified risks to an acceptable level are effective in reducing the number of incidents. Awareness of
security policies and procedures by users, IT staff, and management is also very important.
- Identify precursors and indicators through alerts generated by several types of security
software. Intrusion detection and prevention systems, antivirus software, and file integrity checking
software are valuable for detecting signs of incidents. Each type of software may detect incidents that
the other types of software cannot, so the use of several types of computer security software is highly
recommended. Third – party monitoring services can also be helpful.
- Establish mechanisms for outside parties to report incidents. Outside parties may want to report
incidents to the organization – for example, they may believe that one of the organization's users is
attacking them. Organizations should publish a phone number and email address that outside parties
can use to report such incidents.
- Require a baseline level of logging and auditing on all systems, and a higher baseline level on all
critical systems. Logs from operating systems, services, and applications frequently provide value
during incident analysis, particularly if auditing was enabled. The logs can provide information such
as which accounts were accessed and what actions were performed.
- Profile networks and systems. Profiling measures the characteristics of expected activity levels so
that changes in patterns can be more easily identified. If the profiling process is automated, deviations
from expected activity levels can be detected and reported to administrators quickly, leading to faster
detection of incidents and operational issues.
- Understand the normal behaviors of networks, systems, and applications. Team members who
understand normal behavior should be able to recognize abnormal behavior more easily. This
knowledge can best be gained by reviewing log entries and security alerts; the handlers should
become familiar with the typical data and can investigate the unusual entries to gain more knowledge.
- Create a log retention policy. Information regarding an incident may be recorded in several places.
Creating and implementing a log retention policy that specifies how long log data should be
maintained may be extremely helpful in analysis because older log entries may show reconnaissance
activity or previous instances of similar attacks.
- Perform event correlation. Evidence of an incident may be captured in several logs. Correlating
events among multiple sources can be invaluable in collecting all the available information for an
incident and validating whether the incident occurred.
- Keep all host clocks synchronized. If the devices reporting events have inconsistent clock settings,
event correlation will be more complicated. Clock discrepancies may also cause issues from an
- Maintain and use a knowledge base of information. Handlers need to reference information
quickly during incident analysis; a centralized knowledge base provides a consistent, maintainable
source of information. The knowledge base should include general information, such as data on
precursors and indicators of previous incidents.
- Start recording all information as soon as the team suspects that an incident has occurred.
Every step taken, from the time the incident was detected to its final resolution, should be
documented and timestamped. Information of this nature can serve as evidence in a court of law if
legal prosecution is pursued. Recording the steps performed can also lead to a more efficient,
systematic, and less error-prone handling of the problem.
- Safeguard incident data. It often contains sensitive information regarding such things as
vulnerabilities, security breaches, and users that may have performed inappropriate actions. The team
should ensure that access to incident data is restricted properly, both logically and physically.
- Prioritize handling of the incidents based on the relevant factors. Because of resource limitations,
incidents should not be handled on a first-come, first-served basis. Instead, organizations should
establish written guidelines that outline how quickly the team must respond to the incident and what
actions should be performed, based on relevant factors such as the functional and information impact
of the incident, and the likely recoverability from the incident. This saves time for the incident
handlers and provides a justification to management and system owners for their actions.
Organizations should also establish an escalation process for those instances when the team does not
respond to an incident within the designated time.
- Include provisions regarding incident reporting in the organization's incident response policy.
Organizations should specify which incidents must be reported, when they must be reported, and to
whom. The parties most commonly notified are the CIO, head of information security, local
information security officer, other incident response teams within the organization, and system
- Establish strategies and procedures for containing incidents. It is important to contain incidents
quickly and effectively to limit their business impact. Organizations should define acceptable risks in
containing incidents and develop strategies and procedures accordingly. Containment strategies
should vary based on the type of incident.
- Follow established procedures for evidence gathering and handling. The team should clearly
document how all evidence has been preserved. Evidence should be accounted for at all times. The
team should meet with legal staff and law enforcement agencies to discuss evidence handling, then
develop procedures based on those discussions.
- Capture volatile data from systems as evidence. This includes lists of network connections,
processes, login sessions, open files, network interface configurations, and the contents of memory.
Running carefully chosen commands from trusted media can collect the necessary information
without damaging the system's evidence.
- Obtain system snapshots through full forensic disk images, not file system backups. Disk images
should be made to sanitized write-protectable or write-once media. This process is superior to a file
system backup for investigatory and evidentiary purposes. Imaging is also valuable in that it is much
safer to analyze an image than it is to perform analysis on the original system because the analysis
may inadvertently alter the original.
- Hold lessons learned meetings after major incidents. Lessons learned meetings are extremely helpful in improving security measures and the incident handling process itself.