Attack Chain

1. Attacker gains initial local access to the target Windows system with a standard user account.
2. Attacker leverages existing EFS functionality to interact with encrypted files.
3. Attacker crafts a specific EFS request that triggers the out-of-bounds read vulnerability.
4. The vulnerable EFS component attempts to read data beyond the allocated buffer.
5. The out-of-bounds read operation retrieves sensitive information, such as security tokens or memory addresses of privileged processes.
6. Attacker uses the leaked information to forge or hijack a privileged process.
7. Attacker elevates their privileges to SYSTEM or Administrator.
8. Attacker performs malicious actions, such as installing malware, accessing sensitive data, or creating new privileged accounts.

Impact

Successful exploitation of CVE-2026-26153 allows a local attacker to elevate their privileges on a Windows system. This can lead to complete system compromise, including unauthorized access to sensitive data, installation of malware, and creation of new privileged accounts. The vulnerability affects any system using Windows Encrypting File System (EFS). Given a CVSS score of 7.8, this is considered a high-severity vulnerability, especially in environments where local user accounts are common (e.g., shared workstations, VDI environments).

Recommendation

• Apply the Microsoft patch for CVE-2026-26153 as soon as possible to remediate the vulnerability (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26153).
• Deploy the Sigma rule “Detect EFS Access Followed by Privileged Process Creation” to detect potential exploitation attempts.
• Monitor for suspicious process creation events originating from EFS-related processes, as highlighted in the attack chain.
• Investigate any unusual activity related to EFS file operations using file_event logs.