What is a critical step for incident responders after containing an insider attack?

Regaining access control to all affected systems is a critical step following the containment of an insider attack. This action is essential for restoring normal operations and ensuring that no unauthorized users retain access to the systems. Following an insider attack, the potential for lingering access by the perpetrator or other unauthorized individuals poses a significant security risk. By reestablishing control, incident responders can not only secure the systems but also begin to assess the extent of the breach, recover data, and prevent future incidents.

In contrast, installing firewalls without testing could lead to further vulnerabilities or operational issues, as untested security measures might inadvertently block legitimate users or fail to provide the necessary protection. Immediately shutting down all systems is an extreme response that could halt critical operations and may not be necessary; a more measured approach to regain control and evaluate the situation is preferred. Ignoring the incident in future training would prevent the organization from learning from the attack, thus increasing the likelihood of similar incidents occurring in the future. Thus, prioritizing the restoration of access control is vital for the overall security posture of the organization.