NIST SP 800-61

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.

Handling an Incident

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

Category Definition
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 provides examples of possible information impact categories that describe the extent of information compromise that occurred during the incident. In this table, with the exception of the ‘None' value, the categories are not mutually exclusive and the organization could choose more than one

Table 3-3. Information Impact Categories

Category Definition
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 shows examples of recoverability effort categories that reflect the level of and type of resources required to recover from the incident.

Table 3-4. Recoverability Effort Categories

Category Definition
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

Organizations should also establish an escalation process for those instances when the team does not respond to an incident within the designated time. This can happen for many reasons: for example, cell phones may fail or people may have personal emergencies. The escalation process should state how long a person should wait for a response and what to do if no response occurs. Generally, the first step is to duplicate the initial contact. After waiting for a brief time – perhaps 15 minutes – the caller should escalate the incident to a higher level, such as the incident response team manager. If that person does not respond within a certain time, then the incident should be escalated again to a higher level of management. This process should be repeated until someone responds.