Microsoft Office Excel: Stack-based buffer overflow enables remote code execution
Summary
A stack-based buffer overflow in Microsoft Excel, part of Microsoft 365 Apps, Office LTSC, Office for Mac and Office Online Server, allows an unauthorized attacker to execute code over the network. Exploitation requires user interaction, typically opening a crafted Excel file received by email or download. No privileges are needed and the CVSS score is 8.8 (high). Microsoft has published fixes; no exploitation or public exploit code is known at the time of writing.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the build in the Office security release notes
- Office 365 for Mac: before 16.115.26110837
- Office LTSC 2021: before 16.0.14334.21048
- Office LTSC 2024: before 16.0.17932.21140
- Office LTSC for Mac 2021 and 2024: before 16.115.26110837
- Office Online Server: before 16.0.10417.20236
Fixed in
- Microsoft 365 Apps: current build per https://aka.ms/OfficeSecurityReleases (not stated in the CVE record)
- Office 365 for Mac and Office LTSC for Mac: 16.115.26110837 or later
- Office LTSC 2021: 16.0.14334.21048 or later
- Office LTSC 2024: 16.0.17932.21140 or later
- Office Online Server: 16.0.10417.20236 or later
Workaround
Unknown.
Exploitation
- No evidence of exploitation in the wild found at time of writing
- No public proof-of-concept found
- CISA SSVC: exploitation none, automatable no, technical impact total
Our recommendation
- Update Office and Microsoft 365 Apps to the fixed builds listed above on all endpoints and verify the actual build numbers
- Patch Office Online Server first if it is used and reachable from the internet
- Keep Protected View enabled, block macros and files from the internet, and be cautious with unexpected spreadsheets
- Re-check NVD and the CISA KEV catalog in the coming 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-2026-118717) msrc.microsoft.com
- CVE.org record CVE-2026-118717 www.cve.org
- Strix CVE summary CVE-2026-118717 www.strix.ai
- threatint CVE summary CVE-2026-118717 cve.threatint.com
- Stefan Gossner blog on SharePoint/OOS November 2026 update (third-party) blog.stefan-gossner.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 10 Nov 2026, 21:47.
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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