Microsoft Office Word: Heap-based buffer overflow allows remote code execution
Summary
A heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network. The CVSS vector shows network access, low complexity and no privileges required, but user interaction is needed, most likely by opening a crafted document. Successful exploitation could fully compromise confidentiality, integrity and availability of the affected system.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 before the fixed build (exact build unknown)\n- Microsoft Office LTSC 2021: 16.0.1 before 16.0.14334.21048\n- Microsoft Office LTSC 2024: 16.0.0 before 16.0.17932.21140\n- Microsoft Office 365 for Mac: before 16.115.26110837\n- Microsoft Office LTSC for Mac 2021 and 2024: before 16.115.26110837
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown. Check https://aka.ms/OfficeSecurityReleases\n- Microsoft Office LTSC 2021: 16.0.14334.21048\n- Microsoft Office LTSC 2024: 16.0.17932.21140\n- Microsoft Office 365 for Mac and LTSC for Mac: 16.115.26110837 (verify against Microsoft's advisory)
Workaround
Unknown. No vendor workaround was found in the reviewed sources. Patching is the fix.
Exploitation
- No evidence of exploitation in the wild found at the time of research.\n- No public proof of concept found.\n- The CVSS temporal metric E:U indicates exploit code maturity 'unproven'.\n- Checks were limited; the CISA KEV catalog and MSRC exploitation flag should be re-checked.
Our recommendation
- Patch Microsoft 365 Apps, Office LTSC 2021/2024 and Mac builds in the next regular cycle, with priority.\n- Prioritise staff who open external documents.\n- Verify that the update has reached all endpoints.\n- Keep Protected View enabled and block Office documents from internet and email sources until patched.\n- Monitor the CVE record and MSRC for updates, as NVD analysis is still pending.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- CVE Record CVE-2026-111299 www.cve.org
- Microsoft Security Update Guide CVE-2026-111299 msrc.microsoft.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 10 Nov 2026, 23:16.
Original description (NVD)
Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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