Microsoft Office Word: Heap-based buffer overflow enables code execution
Summary
A heap-based buffer overflow in Microsoft Word, part of Microsoft 365 Apps, Office 365 for Mac and Office LTSC 2021 and 2024, can be used by an attacker to execute code. The CVSS vector (AV:L) requires local access, no privileges and user interaction, typically by opening a crafted document. The vendor title says Remote Code Execution and an unverified third-party entry describes network exploitation, so the attack vector should be confirmed on the MSRC advisory. Microsoft reports no public disclosure and no known exploitation.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed releases
- Office 365 for Mac: before 16.114.26101123
- Office LTSC 2021: 16.0.1 before 16.0.14334.20974
- Office LTSC 2024: 16.0.0 before 16.0.17932.21056
- Office LTSC for Mac 2021 and 2024: before 16.114.26101123
Fixed in
- Install the October 2026 security release (13 October 2026).
- Builds shipped that day per Microsoft release notes: Current Channel 2609 build 20430.20182; Monthly Enterprise Channel 2609 20430.20180, 2608 20326.20232, 2607 20228.20276; Office LTSC 2024 17932.21056; Office LTSC 2021 14334.20974.
- Minimum fixed builds per product should be verified on the MSRC advisory.
Workaround
- Unknown. No vendor workaround was found in the sources reviewed.
- General measures, not documented mitigations for this CVE: keep Protected View enabled for files from the internet or email, and restrict macros and attachments where business allows.
Exploitation
- Microsoft: not publicly disclosed, not exploited, exploitation less likely.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public proof of concept or in-the-wild exploitation found; this does not prove none exists.
Our recommendation
- Deploy the October 2026 Office update on all affected installations.
- Prioritize Office LTSC 2021 installations, which receive no further security updates after October 2026.
- Check Microsoft 365 Apps on Windows 10 for build 2608 (20326.20232) or later.
- Verify the attack vector and minimum builds on the MSRC advisory.
- Restrict opening of untrusted attachments and watch for suspicious Word documents.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC advisory CVE-2026-70220 msrc.microsoft.com
- NVD mirror (OpenCVE) CVE-2026-70220 app.opencve.io
- Microsoft 365 Apps security updates (release notes) learn.microsoft.com
- Microsoft 365 Apps update history by date learn.microsoft.com
- CNA record mirror (Vulners) vulners.com
- VulDB entry 418243 vuldb.com
- CNNVD entry CNNVD-2026-44964909 vulners.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 2 Nov 2026, 04:01.
Original description (NVD)
Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code locally.
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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