Microsoft Office Excel: Remote code execution via heap-based buffer overflow
Summary
Microsoft Office Excel contains a heap-based buffer overflow (CWE-122) that allows an unauthorized attacker to execute code over a network. Exploitation requires that a user opens a manipulated spreadsheet, for example one received by email or downloaded from the internet (UI:R). Microsoft rates the CVSS v3.1 base score at 8.8; NVD analysis was still pending at publication.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 to before the build listed on the Microsoft security release page (aka.ms/OfficeSecurityReleases)
- Office 365 for Mac: before 16.115.26110837
- Office LTSC 2021: 16.0.1 to before 16.0.14334.21048
- Office LTSC 2024: 16.0.0 to before 16.0.17932.21140
- Office LTSC for Mac 2021 and 2024: before 16.115.26110837
- Office Online Server: 16.0.0.0 to before 16.0.10417.20236
Fixed in
- Builds listed as the upper limit of the affected ranges above, according to the CVE record. Verify on the MSRC advisory before relying on them.
- Microsoft 365 Apps for Enterprise: current build from the Microsoft security release page (not stated in the CVE data).
- Office Online Server: included in the November 2026 SharePoint public update, according to a third-party blog.
Workaround
- None known. Microsoft's CVE data points to the security update as the remedy.
Exploitation
- No exploitation known at publication.
- No public proof-of-concept known.
- CISA SSVC: exploitation none, not automatable, total technical impact.
- CVSS temporal exploit code maturity: Unproven (E:U).
Our recommendation
- Update Microsoft 365 Apps, Office LTSC and Office for Mac clients in the November 2026 update cycle, after confirming build numbers on the MSRC advisory.
- Patch any Office Online Server or SharePoint farm in the same cycle. Check first whether the farm has the required permissions fix for the September 2025 CU.
- Check whether Office Online Server or SharePoint is reachable from the internet and prioritise those systems.
- Until patched, do not open untrusted spreadsheets from email or downloads, keep Protected View enabled, and restrict Office file types from the internet.
- Watch for NVD analysis updates and changes to the exploitation status.
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 Response Center advisory CVE-2026-118709 msrc.microsoft.com
- CVE Record CVE-2026-118709 (CVE.org) www.cve.org
- Stefan Gossner blog: SharePoint security fixes November 2026 blog.stefan-gossner.com
- Cybersecurity News: Microsoft November 2026 Patch Tuesday cybersecuritynews.com
- Strix AI CVE-2026-118709 www.strix.ai
- Threatint CVE-2026-118709 cve.threatint.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, 21:52.
Original description (NVD)
Heap-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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