Microsoft Office Excel: Remote code execution via heap-based buffer overflow
Summary
Microsoft Office Excel contains a heap-based buffer overflow that allows an unauthorized attacker to execute code over a network. Exploitation requires that a user opens a specially crafted workbook, typically received by email or as a downloaded file, and interacts with affected features. The code runs in the context of the signed-in user. Microsoft has published security updates.
Affected
- Microsoft 365 Apps for Enterprise (16.0.1 up to the build listed on the Office security releases page)
- Microsoft Office 365 for Mac (1.0.0 before 16.115.26110837)
- Microsoft Office LTSC 2021 (16.0.1 before 16.0.14334.21048)
- Microsoft Office LTSC 2024 (16.0.0 before 16.0.17932.21140, third-party data, not verified against MSRC)
- Microsoft Office LTSC for Mac 2021 and 2024 (before 16.115.26110837, third-party data for 2024 edition, not verified against MSRC)
- Microsoft Office Online Server (16.0.0.0 before 16.0.10417.20236, third-party data, not verified against MSRC)
Fixed in
- Office LTSC 2021: 16.0.14334.21048 (per CVE record)
- Office 365 for Mac and LTSC for Mac: 16.115.26110837 (per CVE record)
- Microsoft 365 Apps for Enterprise: Unknown. Check the Office security releases page and the MSRC update guide.
- Office LTSC 2024 and Office Online Server: builds listed above are from third-party data and must be confirmed against the MSRC table.
Workaround
Unknown. No workaround is documented in the sources reviewed. Microsoft recommends installing the security update.
Exploitation
- No evidence of exploitation in the wild was found.
- No public proof-of-concept was found.
- Microsoft rates exploit code maturity as Unproven (E:U) and report confidence as Confirmed (RC:C).
Our recommendation
- Deploy the November 2026 Office security updates to all affected clients and confirm the installed build numbers.
- Treat this as high priority for Microsoft 365 and LTSC clients, because the CVSS score is 8.8.
- Until patched, keep Protected View enabled for files from the internet and email, and block or restrict Excel files from untrusted senders where feasible.
- Instruct users not to open unsolicited workbooks.
- Monitor for exploitation reports, as the vulnerability was published on the same day as this entry.
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-2026-120789 msrc.microsoft.com
- CVE Record CVE-2026-120789 (CVE.org) www.cve.org
- Strix CVE summary CVE-2026-120789 (third-party) www.strix.ai
- VulDB entry 434115 (third-party) vuldb.com
- Microsoft November 2026 Patch Tuesday roundup 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, 21:27.
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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