Review reviewHigh

CVE-2026-55133

Microsoft Microsoft 365 Apps for Enterprise, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2021

Heap-based buffer overflow in Microsoft Office OneNote allows an unauthorized attacker to execute code locally.

PRIORITY ASSESSMENT

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.30%

Technical severityCVSS 7.8

Heap-based buffer overflow in Microsoft Office OneNote allows an unauthorized attacker to execute code locally.

Product: Microsoft Microsoft 365 Apps for Enterprise, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2021
Affected versions: >= 16.0.1 < https://aka.ms/OfficeSecurityReleases, >= 1.0.0 < 16.111.26071215, >= 16.0.1 < 16.111.26071215, >= 16.0.0 < 16.111.26071215
Fixed versions: No verified fixed-version field is available yet

Confirm exposure before applying a vendor-supported change.

1
Identify
Confirm that Microsoft Microsoft 365 Apps for Enterprise, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2021 and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.