Microsoft Office Word: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code over a network. The vector requires no privileges but user interaction, so an attacker would most likely need a victim to open or interact with a crafted document. The CVSS base score is 8.8 (High).
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 before the fixed build (exact build unknown, see Office security releases page)
- Office LTSC 2021: 16.0.1 before 16.0.14334.21048
- Office LTSC 2024: 16.0.0 before 16.0.17932.21140
- Office 2016 and Office 2019: Unknown, not listed in the CNA record
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown, check https://aka.ms/OfficeSecurityReleases
- Office LTSC 2021: 16.0.14334.21048
- Office LTSC 2024: 16.0.17932.21140
Workaround
Unknown. No workaround or mitigation was found; patching is the available fix.
Exploitation
- No known exploitation in the wild found at the time of research (not confirmed against CISA KEV)
- No public proof of concept found
- The CNA's temporal vector indicates exploit code maturity is unproven (E:U)
- NVD analysis pending
Our recommendation
- Patch Microsoft 365 Apps and Office LTSC 2021/2024 installations as soon as possible using the Microsoft security releases
- Verify the status of Office 2016 and 2019 in the MSRC advisory and patch if affected
- Reduce risk from malicious documents: apply email filtering for attachments, and make users aware of unexpected document attachments or downloads
- Recheck the CISA KEV catalogue and NVD for updates
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-123394 msrc.microsoft.com
- CVE Record: CVE-2026-123394 www.cve.org
- Strix: CVE-2026-123394 www.strix.ai
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, 21:11.
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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