CVE-2021-36934

CVE-2021-36934 is an elevation of privilege vulnerability in Windows caused by overly permissive Access Control Lists (ACLs) on multiple system files, including the Security Accounts Manager (SAM) database. A local attacker who already has the ability to execute low-privileged code on a victim system can leverage the misconfigured ACLs to gain arbitrary code execution with SYSTEM privileges, then install programs, view, change or delete data, or create new accounts with full user rights. Affected products per the CPE data are Windows 10 versions 1809, 1909, 2004, 20H2 and 21H1, with related coverage noting the bug impacts all Windows 10 versions released in the past 2.5 years and also references Windows 11. CISA added the flaw to its Known Exploited Vulnerabilities Catalog on 2022-02-10, confirming in-the-wild exploitation, and EPSS assigns a 67.3% probability of exploitation within 30 days (99th percentile). Mitigation is two-step: installing the security update alone is not sufficient — administrators must also manually delete all shadow copies of system files, including the SAM database, per KB5005357.

What to do: Apply Microsoft's security update per vendor instructions, then follow KB5005357 to manually delete all shadow copies of system files (including the SAM database), because the update alone does not fully mitigate the vulnerability. Restrict or verify ACLs on the System32 config directory and shadow-copy access if shadow-copy deletion cannot be done immediately, and prioritize patching given the flaw's listing in CISA's Known Exploited Vulnerabilities Catalog.