Cisco Secure Endpoint Tampering via SFC Utility

This analytic focuses on detecting the misuse of the System File Checker (sfc.exe) utility with the -unblock parameter, a specific feature integrated within Cisco Secure Endpoint. This functionality is designed to remove system-level blocks that Cisco Secure Endpoint imposes on files or processes identified as potentially malicious. While legitimate use cases exist for troubleshooting and resolving false positives, adversaries can exploit this command to bypass endpoint protection mechanisms. By unblocking files, attackers can facilitate the execution of malware, evade detection, and maintain persistence within the compromised environment. The targeted use of sfc.exe -unblock is a significant indicator of potential security solution tampering.

Attack Chain

1. An attacker gains initial access to a compromised endpoint, possibly through phishing or exploiting a software vulnerability.
2. The attacker identifies a file or process blocked by Cisco Secure Endpoint.
3. The attacker elevates privileges to execute commands with administrative rights.
4. The attacker uses the sfc.exe utility with the -unblock parameter, specifying the blocked file’s path as an argument: sfc.exe /UNBLOCK=<file_path>.
5. SFC removes the block imposed by Cisco Secure Endpoint on the specified file.
6. The attacker executes the previously blocked file, initiating the malicious payload.
7. The malicious payload performs actions such as establishing command and control, lateral movement, or data exfiltration.

Impact

Successful exploitation allows attackers to bypass Cisco Secure Endpoint’s protective measures, enabling the execution of blocked malware or tools. This can lead to a full system compromise, data theft, or disruption of services. The impact is especially severe if critical system files are unblocked, potentially destabilizing the operating system.

Recommendation

• Deploy the Sigma rule Detect Cisco Secure Endpoint File Unblock via SFC to identify instances where sfc.exe is used with the -unblock parameter.
• Investigate any identified instances of sfc.exe -unblock to determine if the action was legitimate and authorized.
• Monitor process execution for any files unblocked via sfc.exe, and correlate with other security events to detect malicious activity.
• Implement additional endpoint monitoring to detect suspicious activity following the use of sfc.exe -unblock.