CVE-2026-109491: Microsoft 365 Apps for Enterprise (high)

Summary

Microsoft Office Word has a use-after-free flaw that lets an unauthorized attacker run code on an affected system. The attacker can reach it remotely, without logging in, but a user must take an action, such as opening a crafted file.

Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.

Read the original description

Use after free in Microsoft Office Word allows an unauthorized attacker to execute code over a network.

cve.now Index

16Pcve.now Index 16 of 100 · methodology v3 · provisional

Exploitation0/40No signal
Exposure7/25Reachable over the network without a login · Unknown: No advisory context yet
Reach?/20Unknown. No tracked technology or package matched
Severity8.5/10CVSS 7.5, total technical impact per CISA
No patch0/5No signal

What would change the score

Would score about 71 if added to CISA KEV
Would score about 66 if CISA's SSVC rates exploitation active
Would score about 31 if advisories confirm default setups are exposed

How the score works · Rankings

What to do

Upgrade to a fixed version: Microsoft Office 365 for Mac 16.115.26110837 · Microsoft Office LTSC 16.0.14334.21048, 16.0.17932.21140 · Microsoft Office LTSC for Mac 16.115.26110837.

Check your systems with an agent

Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.

Check whether my systems are affected by CVE-2026-109491 (Microsoft Office Word Remote Code Execution Vulnerability), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-109491 (entry last updated 2026-11-10):
Affected:
- Microsoft Microsoft 365 Apps for Enterprise: from 16.0.1
- Microsoft Microsoft Office 365 for Mac: from 1.0.0, fixed in 16.115.26110837
- Microsoft Microsoft Office LTSC 2021: from 16.0.1, fixed in 16.0.14334.21048
- Microsoft Microsoft Office LTSC 2024: from 16.0.0, fixed in 16.0.17932.21140
- Microsoft Microsoft Office LTSC for Mac 2021: from 16.0.1, fixed in 16.115.26110837
- Microsoft Microsoft Office LTSC for Mac 2024: from 16.0.0, fixed in 16.115.26110837
Fixed versions: 16.115.26110837, 16.0.14334.21048, 16.0.17932.21140.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-109491 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-109491 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-109491
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Entry: https://cve.now/CVE-2026-109491
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-109491.

Timeline

Nov 10, 2026, 6:15 PM UTCCVE published
Nov 10, 2026, 8:42 PM UTCFirst seen by cve.now
Nov 10, 2026, 8:48 PM UTCCISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: total
Nov 10, 2026, 11:47 PM UTCRecord last updated

Affected versions

Microsoft Microsoft 365 Apps for Enterprise
From 16.0.1
Microsoft Microsoft Office 365 for Mac
From 1.0.0 · fixed in 16.115.26110837
Microsoft Microsoft Office LTSC 2021
From 16.0.1 · fixed in 16.0.14334.21048
Microsoft Microsoft Office LTSC 2024
From 16.0.0 · fixed in 16.0.17932.21140
Microsoft Microsoft Office LTSC for Mac 2021
From 16.0.1 · fixed in 16.115.26110837
Microsoft Microsoft Office LTSC for Mac 2024
From 16.0.0 · fixed in 16.115.26110837

Evidence 3

Vendor advisory · 1

Establishes: Affected and fixed versions.

Patch
msrc.microsoft.com · update-guide/vulnerability/CVE-2026-109491

CVE record · 2

Establishes: The identifier and description.

Record
CVE List · CVE-2026-109491
Record
NVD · CVE-2026-109491

Corrections

None so far.

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Questions about CVE-2026-109491

Is CVE-2026-109491 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data

Which versions are affected by CVE-2026-109491?

Microsoft 365 Apps for Enterprise: from 16.0.1. Microsoft Office 365 for Mac: from 1.0.0 before 16.115.26110837. Microsoft Office LTSC 2021: from 16.0.1 before 16.0.14334.21048. Microsoft Office LTSC 2024: from 16.0.0 before 16.0.17932.21140. Microsoft Office LTSC for Mac 2021: from 16.0.1 before 16.115.26110837. 1 more package is listed on the page.Source: cve.now feed data

How do I fix CVE-2026-109491?

Upgrade to a fixed version: Microsoft Office 365 for Mac 16.115.26110837 · Microsoft Office LTSC 16.0.14334.21048, 16.0.17932.21140 · Microsoft Office LTSC for Mac 16.115.26110837.Source: cve.now feed data

Microsoft Office Word Remote Code Execution Vulnerability