Microsoft Word: Remote code execution via stack-based buffer overflow
Summary
A stack-based buffer overflow in Microsoft Word, part of Microsoft 365 Apps and Office, allows code execution. An attacker who gets a victim to open a crafted Word document can run code with the victim's rights. No privileges are required, but user interaction is needed. The CVSS 3.1 base score is 8.8 (High).
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build listed in the Microsoft advisory
- Microsoft Office 365 for Mac: versions 1.0.0 to before 16.114.26101123
- Office LTSC 2021: 16.0.1 to before 16.0.14334.20974
- Office LTSC 2024: 16.0.0 to before 16.0.17932.21056
- Office LTSC for Mac 2021: 16.0.1 to before 16.114.26101123
- Office LTSC for Mac 2024: 16.0.0 to before 16.114.26101123
Fixed in
- Install the Microsoft Office security update released on October 13, 2026, for each affected edition.
- Exact fixed builds: see the Microsoft Security Update Guide entry for CVE-2026-83891.
Workaround
- No vendor-published workaround found.
- Interim risk reduction (own recommendation, not from a vendor source): block or sandbox untrusted Office attachments at the mail gateway, keep Protected View enabled, and restrict macro and file-type settings where business needs allow.
Exploitation
- CISA SSVC data: Exploitation none, Automatable no.
- Not listed in CISA KEV according to a third-party tracker; EPSS unknown.
- A Qualys review of the October 2026 Patch Tuesday mentions an exploited fix, but does not name this CVE. Unconfirmed.
- No public proof of concept found.
Our recommendation
- Patch Microsoft 365 Apps and Office installations now, starting with users who handle email attachments and external documents.
- Verify the installed build against the Microsoft advisory.
- Keep Protected View enabled and filter or sandbox untrusted Office attachments until patching is complete.
- Monitor for unusual Word process activity and warn users not to open unexpected documents.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-83891 msrc.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- OpenCVE: CVE-2026-83891 app.opencve.io
- Strix: CVE-2026-83891 www.strix.ai
- Qualys: Microsoft Patch Tuesday October 2026 review blog.qualys.com
- GitHub tracker issue for CVE-2026-83891 github.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 31 Oct 2026, 18:26.
Original description (NVD)
Stack-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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