Microsoft Office Excel: Remote Code Execution through stack-based buffer overflow
Summary
Microsoft Office Excel contains a stack-based buffer overflow (CWE-121). An unauthorized attacker can execute code over the network. The attack requires a user to open a crafted file, for example an email attachment or a file from a file share.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 before the build listed on the MSRC advisory (exact build unknown)
- Office 365 for Mac: 1.0.0 before 16.115.26110837
- Office LTSC 2021: 16.0.1 before 16.0.14334.21048
- Office LTSC 2024: 16.0.0 before 16.0.17932.21140 (unconfirmed, from third-party source)
- Office LTSC for Mac 2021 and 2024: before 16.115.26110837 (unconfirmed, from third-party source)
- Office Online Server: 16.0.0.0 before 16.0.10417.20236 (unconfirmed, from third-party source)
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown.
- Office 365 for Mac: 16.115.26110837
- Office LTSC 2021: 16.0.14334.21048
- Office LTSC 2024: Unknown from the CVE record; third-party source lists 16.0.17932.21140.
- Office Online Server: Unknown from the CVE record; third-party source lists 16.0.10417.20236.
Workaround
Unknown. No vendor-documented workaround was found. General Office hardening such as keeping Protected View enabled, blocking macros and external content, and using Attack Surface Reduction rules limits document-borne attacks.
Exploitation
- No exploitation in the wild found at publication.
- No public proof of concept found; VulDB states no exploit is available.
- Not listed in CISA KEV as far as known.
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
Our recommendation
- Patch Microsoft 365 Apps and Office LTSC clients through the November 2026 update cycle, and verify the fixed build on the MSRC advisory.
- Check whether SharePoint Server or Office Online Server systems are in use and internet-facing.
- Restrict risky attachments and enforce Protected View.
- Re-check exploitation status and KEV listing over the next days.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Microsoft Office Excel
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Microsoft Office
- Updates (KB)
- KB5002946
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-118731 msrc.microsoft.com
- CVE Record CVE-2026-118731 (CVE.org) www.cve.org
- VulDB entry 434138 vuldb.com
- SharePoint security fixes November 2026 PU (Stefan Gossner) blog.stefan-gossner.com
- Strix CVE-2026-118731 (third-party, unverified) 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, 21:42.
Original description (NVD)
Stack-based buffer overflow in Microsoft Office Excel 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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