Microsoft Office Word: Remote code execution via stack-based buffer overflow
Summary
A stack-based buffer overflow in Microsoft Office Word (CWE-121) allows an unauthorized attacker to execute code over a network. The attack requires the victim to interact, most likely by opening a crafted document such as an email attachment or a download. The CNA rates the flaw CVSS 8.8 (High); a VulDB entry rates it 5.5 (Medium), and the NVD status is inconsistent across sources.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 to below the build listed at https://aka.ms/OfficeSecurityReleases (exact fixed build unknown)
- Office 365 for Mac: 1.0.0 to below 16.114.26101123
- Office LTSC 2021 (Windows): 16.0.1 to below 16.0.14334.20974
- Office LTSC 2024 (Windows): 16.0.0 to below 16.0.17932.21056
- Office LTSC for Mac 2021: 16.0.1 to below 16.114.26101123
- Office LTSC for Mac 2024: 16.0.0 to below 16.114.26101123
Fixed in
- Office LTSC 2021 (Windows): 16.0.14334.20974
- Office LTSC 2024 (Windows): 16.0.17932.21056
- Office 365 for Mac and Office LTSC for Mac: 16.114.26101123
- Microsoft 365 Apps for Enterprise: Unknown. Take the build from the MSRC advisory or the Office security release notes.
Workaround
Unknown. No workaround was found in the sources. Check the MSRC advisory for mitigation text.
Exploitation
- CISA SSVC in the CVE record: exploitation none, automatable no.
- Not listed in CISA KEV, according to one aggregator (thehackerwire.com).
- No public proof-of-concept found, according to one aggregator; not confirmed by a primary source.
- No in-the-wild exploitation known from the sources.
Our recommendation
- Patch Microsoft 365 Apps, Office LTSC and Office for Mac according to the MSRC advisory.
- Prioritise systems that regularly open external documents or email attachments.
- Keep Protected View enabled for files from the internet and email.
- Where practical, restrict inbound Office document attachments.
- Verify the fixed builds on the MSRC page before rollout, as the sources are third-party mirrors.
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-2026-108440 msrc.microsoft.com
- OpenCVE: CVE-2026-108440 app.opencve.io
- Strix: CVE-2026-108440 www.strix.ai
- ThreatInt: CVE-2026-108440 cve.threatint.com
- VulDB: CVE-2026-108440 vuldb.com
- TheHackerWire: CVE-2026-108440 www.thehackerwire.com
- OffSeq Radar: CVE-2026-108440 radar.offseq.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, 16:21.
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.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.