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CVE-2026-77503 Microsoft CVE debrief

A Windows NTFS Elevation of Privilege Vulnerability exists due to an out-of-bounds read in Windows NTFS, allowing local privilege escalation. Multiple Windows versions are affected, including Windows 10, Windows 11, and Windows Server editions. The vulnerability allows an unauthorized attacker to elevate privileges locally. Defenders should prioritize patching affected Windows systems, especially those exposed to local unauthorized access. The CVE Program and NVD provide official records of the vulnerability.

Vendor
Microsoft
Product
Windows 10 Version 1607
CVSS
HIGH 8.4
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-08
Original CVE updated
2026-10-08
Advisory published
2026-09-08
Advisory updated
2026-10-08

Who should care

Defenders responsible for Windows systems, especially those exposed to local unauthorized access, should assess exposure and apply patches. This includes administrators of Windows 10, Windows 11, and Windows Server editions. They should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.

Why it matters

CVE-2026-77503 is a Windows NTFS Elevation of Privilege Vulnerability that allows local privilege escalation. Defenders should prioritize patching affected Windows systems.

  • Local privilege escalation is possible
  • Patching affected systems is necessary
  • Verify system exposure and apply patches

Technical summary

The vulnerability exists due to an out-of-bounds read in Windows NTFS, allowing an unauthorized attacker to elevate privileges locally. Affected versions include Windows 10 Version 1607, Windows 10 Version 1809, Windows 10 Version 21H2, Windows 10 Version 22H2, Windows 11 version 23H2, Windows 11 Version 23H2, Windows 11 Version 24H2, Windows 11 Version 25H2, Windows 11 version 26H1, Windows Server 2012, Windows Server 2012 (Server Core installation), Windows Server 2012 R2, Windows Server 2012 R2 (Server Core installation), Windows Server 2016, Windows Server 2016 (Server Core installation), Windows Server 2019, Windows Server 2019 (Server Core installation), Windows Server 2022, Windows Server 2025, and Windows Server 2025 (Server Core installation).

Defensive priority

Defenders should prioritize patching affected Windows systems, especially those exposed to local unauthorized access.

Recommended defensive actions

  • Patch affected Windows systems
  • Verify system exposure and apply patches
  • Monitor for unauthorized access attempts

Evidence notes

The CVE Program and NVD provide official records of the vulnerability. Microsoft has released a patch for the vulnerability. The vulnerability exists due to an out-of-bounds read in Windows NTFS, allowing an unauthorized attacker to elevate privileges locally. Affected versions include Windows 10 Version 1607, Windows 10 Version 1809, Windows 10 Version 21H2, Windows 10 Version 22H2, Windows 11 version 23H2, Windows 11 Version 23H2, Windows 11 Version 24H2, Windows 11 Version 25H2, and

Sources and references

Verified primary and authoritative sources

  • CVE-2026-77503 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-77503

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

  • CVE-2026-77503 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-77503

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

Supplemental references

  • Windows NTFS Elevation of Privilege Vulnerability

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/77xxx/CVE-2026-77503.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-77503

    Supplemental source - vendor-advisory, patch

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.