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CVE-2026-77894 Microsoft CVE debrief

A race condition vulnerability in Windows Installer allows an authorized attacker to elevate privileges locally. Multiple Windows versions and server releases are affected. This vulnerability, CVE-2026-77894, is a high-severity issue that defenders and system administrators should prioritize for patching, especially for systems with local access. The vulnerability's impact includes local privilege escalation, necessitating immediate assessment and patching of affected systems, including multiple versions of Windows 10, Windows 11, and Windows Server releases.

Vendor
Microsoft
Product
Windows 10 Version 1607
CVSS
HIGH 7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-08
Original CVE updated
2026-09-16
Advisory published
2026-09-08
Advisory updated
2026-09-16

Who should care

Defenders and system administrators responsible for Windows systems, especially those with local access, should assess exposure and apply patches immediately.

Why it matters

CVE-2026-77894 is a high-severity vulnerability in Windows Installer that allows local privilege escalation. Defenders and system administrators should assess exposure, especially for systems with local access, and apply patches immediately. Multiple Windows versions and server releases are affected, requiring inventory and verification.

  • Local privilege escalation possible for authorized attackers
  • Patching required for multiple Windows versions and server releases
  • Inventory and verification of Windows systems necessary

Technical summary

The vulnerability is a race condition in Windows Installer that allows an authorized attacker to elevate privileges locally. The CVSS score is 7 (High). Affected systems include multiple versions of Windows 10, Windows 11, and Windows Server releases.

Defensive priority

Apply patches immediately for Windows systems, especially those with local access.

Recommended defensive actions

  • Apply patches for Windows 10, Windows 11, and Windows Server
  • Verify and apply updates for Windows Server 2012, 2016, 2019, 2022, and 2025
  • Inventory Windows systems for exposure, especially those with local access

Evidence notes

The CVE record and NVD detail page provide information on the vulnerability, including its description, CVSS score, and affected systems. The CVE record was published on 2026-09-08T18:20:39.367Z and has not been modified since then. The NVD entry is currently Analyzed. There is also a patch and vendor advisory from Microsoft (ref-3) that provides additional details on the vulnerability and recommended actions for defenders. Defenders should verify the affected scope, severity, and to

Sources and references

Verified primary and authoritative sources

  • CVE-2026-77894 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-77894

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-77894 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-77894

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.