Attack Chain

1. Attacker gains local access to a Windows system.
2. Attacker identifies the RDLS service running on the system.
3. Attacker crafts a malicious request to a critical function lacking authentication.
4. The vulnerable RDLS service processes the request without proper authentication.
5. Attacker leverages the improperly handled request to modify system configurations.
6. The system configuration changes grant the attacker elevated privileges.
7. The attacker executes arbitrary code with SYSTEM privileges.

Impact

Successful exploitation of CVE-2026-26159 grants a local attacker elevated privileges, potentially leading to complete system compromise. The attacker can install programs, view, change, or delete data, or create new accounts with full user rights. This vulnerability poses a significant risk to systems where local users are not fully trusted, such as shared workstations or environments with weak access controls. The impact is limited to local privilege escalation and does not enable remote code execution without prior local access.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-26159 as soon as possible to remediate the vulnerability (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26159).
• Monitor for suspicious process creation events associated with the Remote Desktop Licensing Service to detect potential exploitation attempts using the provided Sigma rules.
• Implement the provided Sigma rule to detect suspicious modifications of system configurations, which is a required step to achieve local privilege escalation.