CVE-2026-20805

CVE-2026-20805 is an information disclosure flaw (CWE-200) in Desktop Windows Manager (DWM) that exposes sensitive information to an unauthorized actor. An authorized attacker with local access and low privileges can trigger the flaw without user interaction and read sensitive data to which they should not have access. All supported Windows client versions from Windows 10 1607 through Windows 11 25H2 and Windows Server from 2012 through 2022 23H2 are affected, meaning essentially the entire installed Windows estate. The flaw was fixed in Microsoft's January 2026 Patch Tuesday release and was added to CISA's Known Exploited Vulnerabilities catalog on 2026-01-13, confirming exploitation in the wild, though ransomware use is unknown and no public proof-of-concept is available.

What to do: Deploy the January 2026 Microsoft security updates (Patch Tuesday) for every affected Windows 10/11 client and Windows Server release, prioritizing internet-facing and multi-user systems. Federal agencies must apply the updates per BOD 22-01 timelines following the KEV listing on 2026-01-13; other organizations should treat this as a priority patch given confirmed in-the-wild exploitation. After patching, review local account activity on Windows endpoints for signs of low-privileged information gathering, and note that patching is the primary mitigation since the flaw requires only local access.