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PatchSiren cyber security CVE debrief

CVE-2026-77898 Microsoft CVE debrief

CVE-2026-77898 is a high-severity vulnerability in Microsoft Office, with a CVSS score of 7.5. It allows an unauthorized attacker to execute code over a network, potentially leading to significant impacts on affected systems. The vulnerability is a heap-based buffer overflow in Microsoft Office, which could allow an attacker to execute code over a network. Defenders responsible for managing Microsoft Office installations, especially in network-exposed environments, should prioritize patching and verifying the vulnerability status of affected systems. The CVE record and NVD entry provide details on the vulnerability, including its CVSS score and vector. However, specific version of

Vendor
Microsoft
Product
Microsoft 365 Apps for Enterprise
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-08
Original CVE updated
2026-09-17
Advisory published
2026-09-08
Advisory updated
2026-09-17

Who should care

Defenders responsible for managing Microsoft Office installations, especially in network-exposed environments, should prioritize patching and verifying the vulnerability status of affected systems.

Why it matters

CVE-2026-77898 is a high-severity vulnerability in Microsoft Office that could allow code execution over a network. Defenders should prioritize patching and verifying the vulnerability status of affected systems, especially in network-exposed environments.

  • Potential code execution over a network
  • High severity vulnerability with CVSS score of 7.5
  • Affected systems may require immediate patching and verification

Technical summary

The vulnerability is a heap-based buffer overflow in Microsoft Office, which could allow an attacker to execute code over a network. The CVSS score is 7.5, indicating a high severity. The vulnerability affects various versions of Microsoft Office, including Office 2019, Office 2021, and Office 2024.

Defensive priority

Defenders should prioritize patching and verifying the vulnerability status of Microsoft Office installations, especially in network-exposed environments.

Recommended defensive actions

  • Apply patches provided by Microsoft for affected Office versions
  • Verify vulnerability status of Microsoft Office installations
  • Monitor network exposure and restrict access to Office applications
  • Review and update incident response plans for potential code execution attacks

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its CVSS score and vector. However, specific version information and exploitation details are limited.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-77898 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-77898

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

  • CVE-2026-77898 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-77898

    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.