Certified: The CISM Prepcast

Welcome to The Bare Metal Cyber CISM Prepcast. This series helps you prepare for the exam with focused explanations and practical context.
Eradication is the phase in the incident response process that turns containment into a meaningful transition toward recovery. Its core purpose is to completely remove all traces of malicious activity—whether that activity was introduced by malware, unauthorized users, or exploited system vulnerabilities. During eradication, the organization eliminates the root cause of the incident, clears out compromised files, terminates unauthorized access, and shuts down any mechanisms the threat actor could use to return. It prepares affected systems for safe restoration and a return to normal business operations. It ensures that the environment is free of persistent threats and latent vulnerabilities that could lead to reinfection. More than just cleanup, eradication builds the clean baseline upon which recovery actions must stand. If this step is skipped or poorly executed, recovery becomes risky, unreliable, or even dangerous. The eradication phase supports not only immediate restoration but also future monitoring and assurance by ensuring that all known issues have been addressed before systems are reintroduced into production environments.
The timing of eradication must be deliberate. It follows containment and often overlaps with the initial phases of investigation. Before any eradication actions are taken, the incident response team must have high confidence that all relevant indicators of compromise have been identified. These indicators may include file hashes, registry entries, IP addresses, user accounts, scheduled tasks, or injected scripts. If eradication begins too soon, before forensic analysis is complete or before the full scope of compromise is known, critical evidence may be lost or hidden threats may remain. The investigation must guide eradication—not the other way around. Coordination is crucial. Eradication teams must work closely with forensic analysts to avoid disrupting volatile data or erasing evidence needed for regulatory or legal purposes. Each eradication step must be planned based on the nature of the incident and the criticality of the systems involved. Systems with high business impact or sensitive data may require more conservative steps and staged rollback procedures. Ultimately, timing eradication correctly is what ensures the process eliminates threats without damaging visibility or undermining trust in the response process.
Malware eradication techniques are some of the most well-established in the cybersecurity domain. The most basic step is to remove all malicious files, binaries, scripts, and associated artifacts from infected systems. This can include deletion of payloads, quarantine of suspicious files, or manual removal of registry entries and scheduled tasks. Endpoint protection tools—whether antivirus, EDR, or XDR platforms—are typically used to scan and clean devices. These tools may offer automated cleanup routines or guided workflows for incident responders. In some cases, clean versions of compromised files or system images must be restored from known-good backups. These backups must be validated to ensure they were not contaminated prior to the attack. Patch management is another essential part of eradication—any vulnerabilities that were exploited during the infection must be patched to prevent recurrence. Additionally, persistence mechanisms must be neutralized. These may include startup scripts, hidden services, modified system files, or rogue cron jobs that allow the threat to reappear even after the visible malware is removed.
When an incident involves unauthorized access or exploitation of system weaknesses, the eradication process focuses on eliminating the access vectors and restoring trust in system integrity. The first step is to revoke any compromised credentials. This includes resetting passwords, rotating service accounts, and revoking session tokens. If privilege escalation or root-level access is suspected, affected systems may need to be re-imaged entirely. Reimaging ensures that backdoors, keyloggers, or hidden malware components are wiped along with the rest of the operating environment. Any unauthorized user accounts must be identified and removed, and any inappropriate permission grants must be reversed. In some cases, entire systems or applications that were exploited may need to be decommissioned, especially if they are outdated, unpatchable, or no longer trusted. Targeted scans should be conducted to identify and confirm the removal of any backdoors or unauthorized services that were installed during the attack. These steps are especially important when the attack involved insider activity or the use of compromised administrative credentials.
In network and cloud environments, eradication requires a broader set of controls and careful attention to interconnectivity. Malicious IP addresses, command-and-control domains, or suspicious communication channels must be blocked at the firewall, proxy, or DNS level. In cloud platforms, unauthorized virtual machines, containers, or workloads should be suspended or deleted. Investigators must check for rogue API tokens, access keys, or service accounts that may have been created or exploited during the incident. These must be removed or rotated immediately. Firewall and routing rules should be audited and reconfigured as needed to close off exploited paths. DNS settings should be examined to ensure there are no redirects, poisonings, or manipulated entries. Key stores, identity providers, and logging platforms must be reviewed for unusual activity, failed login attempts, or residual access permissions. All network and cloud eradication efforts must be carefully tracked to ensure they do not interfere with legitimate services or create downstream disruptions. This is especially challenging in multi-tenant, multi-cloud, or hybrid environments where visibility is often fragmented.
Validation is a required step to confirm that eradication was successful. Simply executing cleanup steps is not enough. Incident responders must return to all known infected systems and verify that every indicator of compromise has been removed. Logs must be reviewed for any signs of reinfection, missed activity, or lingering anomalies. Rescanning with multiple tools—such as combining antivirus, EDR, vulnerability scanners, and manual reviews—is often necessary to confirm a clean state. Patched systems should be tested to ensure vulnerabilities have been fully closed and that no backdoors remain. Threat intelligence should also be used during validation. If specific tactics, techniques, or procedures were associated with the attacker, responders must verify that no residual signs of those methods remain. This includes checking for common persistence strategies, hidden malware payloads, or covert communication methods. If even one compromised system remains unchecked, the entire eradication effort can be undermined by a silent reactivation or lateral reinfection event.
Because eradication efforts often affect multiple teams and system owners, communication must be well-organized. IT operations, information security, helpdesk personnel, and affected business units must work together to execute eradication without confusion or delay. All eradication steps must be logged and coordinated with change management teams. If reboots, patching, or system resets are involved, operations must approve and schedule those actions to minimize disruption. Legal and compliance teams must be informed if eradication involves systems or data subject to forensic preservation. In such cases, alternative steps may be required to balance cleanup with evidentiary integrity. Every eradication action must be documented thoroughly for audit trails and post-incident analysis. At the same time, the recovery team must be prepared to move forward once eradication is confirmed. Coordination ensures that eradication does not exist in a vacuum but instead transitions smoothly into the next phase of incident recovery and system revalidation.
Like all complex processes, eradication is not without challenges. Incomplete detection can result in missed indicators of compromise, allowing artifacts or threat actors to persist. In some cases, the tools available may not be able to scan every location or system, leaving blind spots. Business continuity needs may also interfere with eradication—organizations may be hesitant to reimage systems or disable services that are still in use. In these cases, response teams must balance the need for thoroughness with the reality of operational pressure. There is also the risk of attackers attempting to re-enter the environment during or after eradication if the same vulnerabilities exist or if access was not fully closed. In cloud and third-party environments, limited visibility and shared responsibility can prevent the response team from executing full remediation. User resistance may also delay endpoint cleanup efforts, especially in cases where executive devices or unmanaged personal devices are involved. These challenges must be anticipated in the planning process and mitigated through clear policies, layered controls, and regular testing.
Following eradication, organizations must implement hardening measures to reduce the risk of recurrence. All affected systems should be patched to remove the exploited vulnerabilities, and this effort should extend to similar systems that share the same exposure. Configuration settings should be reviewed and adjusted to reflect current security best practices. Authentication mechanisms should be strengthened with measures like multifactor authentication, stricter password policies, or conditional access controls. Network segmentation can help reduce the scope of future incidents by limiting lateral movement opportunities. Detection rules and monitoring coverage should be updated to include new indicators of compromise or tactics observed during the attack. These improvements not only reduce the likelihood of reinfection, but they also demonstrate a commitment to resilience and continuous learning.
Eradication must be formally integrated into incident response planning. Playbooks should include detailed eradication steps for common attack types—malware, phishing, credential theft, or cloud exploitation. Teams should maintain a validated library of scripts, tools, and platform-specific instructions for performing cleanup actions. Roles and approval steps for actions like system reimaging, service restarts, or credential revocation should be predefined to avoid delays during incidents. Eradication activities should align with recovery timelines and business impact thresholds—ensuring that cleanup is fast enough to support restoration, but thorough enough to ensure confidence. Above all, eradication must be treated as a critical and formal phase of response, not an afterthought or optional activity. Its success determines whether recovery will be clean and sustainable or compromised and short-lived.
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