Microsoft Office Word: Heap-based buffer overflow leading to remote code execution
Summary
A heap-based buffer overflow in Microsoft Word, part of Microsoft 365 Apps, Office LTSC 2021/2024 and Office for Mac, allows an unauthorized attacker to execute code over the network. The attack requires a user to open a crafted document, which is typically delivered by email or download. Successful exploitation would run code with the privileges of the logged-in user, with high impact on confidentiality, integrity and availability.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build listed in the MSRC update guide (exact build unknown)
- Office LTSC 2021: 16.0.1 to below 16.0.14334.20974
- Office LTSC 2024: 16.0.0 to below 16.0.17932.21056 (unverified, third-party source only)
- Office for Mac 365 and LTSC for Mac 2021/2024: 16.0.0 or 16.0.1 to below 16.114.26101123
Fixed in
- Microsoft 365 Apps: October 13, 2026 security update (exact build unknown, see MSRC)
- Office LTSC 2021: 16.0.14334.20974 or later
- Office LTSC 2024: 16.0.17932.21056 or later (unverified)
- Office for Mac: 16.114.26101123 or later (Microsoft release notes list October 14, 2026)
Workaround
Unknown.
Exploitation
- CISA SSVC: Exploitation none, Automatable no
- Microsoft exploit maturity: unproven (E:U)
- Not in CISA KEV catalog at time of research
- No public proof of concept found
Our recommendation
- Install the October 2026 Office security update on all affected Word installations
- Prioritize users who open documents from external sources
- Check the MSRC update guide for exact fixed builds and any interim mitigations
- Warn users about unexpected document attachments and downloads
- Verify patch status with your update management tool
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-88186 msrc.microsoft.com
- Microsoft 365 Apps security update release notes learn.microsoft.com
- Office for Mac release notes learn.microsoft.com
- Vulners CVE List record (CNA data) vulners.com
- Vulners VulnCheck/CISA SSVC enrichment vulners.com
- OpenCVE: CVE-2026-88186 app.opencve.io
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, 18:02.
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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