Microsoft Office Excel: Remote Code Execution via heap-based buffer overflow
Summary
A heap-based buffer overflow (CWE-122) in Microsoft Excel, part of Microsoft 365 Apps, Office LTSC and Office for Mac, allows an unauthorized attacker to execute code over the network. The attacker needs a victim to open a crafted workbook, for example one received by email or downloaded from the internet. Successful exploitation would run code in the user's context with high impact on confidentiality, integrity and availability (CVSS 3.1: 8.8).
Affected
- Microsoft 365 Apps for Enterprise: from 16.0.1 (exact range per Microsoft's advisory)
- Office 365 for Mac: before 16.115.26110837
- Office LTSC 2021: before 16.0.14334.21048
- Office LTSC 2024: from 16.0.0, fixed build unverified (see Fixed)
- Office LTSC for Mac 2021 and 2024: before 16.115.26110837 (per third-party tracker, unverified)
- Office Online Server: from 16.0.0.0, before 16.0.10417.20236 (per third-party tracker, unverified)
Fixed in
- Microsoft 365 Apps for Enterprise: fixed build referenced on Microsoft's Office security releases page (build number not confirmed)
- Office 365 for Mac: 16.115.26110837
- Office LTSC 2021: 16.0.14334.21048
- Office LTSC 2024: 16.0.17932.21140 (from third-party trackers, unverified)
- Office LTSC for Mac 2021 and 2024: 16.115.26110837 (unverified)
- Office Online Server: 16.0.10417.20236 (unverified)
Workaround
Unknown. No workaround or mitigation is documented by the sources reviewed. Patching is the fix.
Exploitation
- No evidence of exploitation in the wild found for this CVE.
- Microsoft's CVE record gives exploit code maturity as unproven (E:U).
- No public proof of concept found.
- Not found in the CISA KEV catalog at the time of research.
Our recommendation
- Patch Microsoft 365 Apps and Office LTSC to the fixed builds in the November 2026 update, following Microsoft's advisory for exact build numbers.
- Prioritise systems that receive external spreadsheets from customers, suppliers or email.
- Until patched, keep Protected View enabled for files from the internet or email, restrict macros, and quarantine spreadsheets from unknown senders.
- Check the CISA KEV catalog and NVD for changes to the exploitation status.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Critical
- 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-2026-120786 msrc.microsoft.com
- CVE Record CVE-2026-120786 (CVE.org) www.cve.org
- Strix: CVE-2026-120786 (third-party, unverified builds) www.strix.ai
- Microsoft November 2026 Patch Tuesday overview (Cybersecurity News) cybersecuritynews.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, 21:32.
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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