PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-55031 Microsoft CVE debrief

Microsoft Excel Remote Code Execution Vulnerability allows an unauthorized attacker to execute code locally due to an out-of-bounds read in Microsoft Office Excel. This vulnerability has a CVSS score of 7.8 and is classified as HIGH severity. The vulnerability affects Microsoft Office Excel, allowing attackers to execute code locally. Defenders should prioritize patching vulnerable versions and restrict user interaction with untrusted files. The CVE Program and NVD provide official records of the vulnerability, and Microsoft has released a patch for this vulnerability.

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-10-08
Advisory published
2026-07-14
Advisory updated
2026-10-08

Who should care

Defenders responsible for Microsoft Office and Excel deployments should assess exposure and prioritize patching, especially in environments where user interaction with untrusted files is common.

Why it matters

CVE-2026-55031 is a high-severity vulnerability in Microsoft Excel that allows remote code execution. Defenders should prioritize patching vulnerable versions and restrict user interaction with untrusted files.

  • Potential code execution requires verification from official sources
  • Patching vulnerable versions is a defensive priority
  • Restricting user interaction with untrusted files can mitigate risk

Technical summary

The vulnerability is caused by an out-of-bounds read in Microsoft Office Excel, allowing an unauthorized attacker to execute code locally. The vulnerability affects Microsoft Office Excel and has a CVSS score of 7.8. Defenders should prioritize patching vulnerable Microsoft Excel and Office versions, especially in environments where user interaction with untrusted files is common.

Defensive priority

Defenders should prioritize patching vulnerable Microsoft Excel and Office versions, especially in environments where user interaction with untrusted files is common.

Recommended defensive actions

  • Patch vulnerable Microsoft Excel and Office versions
  • Restrict user interaction with untrusted files
  • Monitor for suspicious activity

Evidence notes

The CVE Program and NVD provide official records of the vulnerability. Microsoft has released a patch for this vulnerability. The vulnerability has been verified by official sources, and defenders should verify affected scope, severity, and vendor guidance. The vulnerability affects Microsoft Office Excel, and defenders should review compensating controls for exposed systems while remediation is scheduled and verified.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-55031 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-55031

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

  • CVE-2026-55031 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-55031

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

Supplemental references

  • Microsoft Excel Remote Code Execution Vulnerability

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/55xxx/CVE-2026-55031.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55031

    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.