Microsoft Office Excel: Heap-based buffer overflow leads to remote code execution
Summary
A heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network. The attack requires that a user opens a manipulated file, for example a spreadsheet received by email or download. No privileges and no internet-facing service are needed, and a successful attack could compromise the user's session and data.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 to before the build listed at https://aka.ms/OfficeSecurityReleases
- Office 365 for Mac: 1.0.0 to 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: 16.0.1 to before 16.115.26110837
- Office LTSC for Mac 2024: 16.0.0 to before 16.115.26110837
- Office Online Server: 16.0.0.0 to before 16.0.10417.20236 (listed in the CVE record, to be verified on MSRC)
Fixed in
- Office LTSC 2021: 16.0.14334.21048
- Office 365 for Mac and LTSC for Mac: 16.115.26110837
- Office LTSC 2024: 16.0.17932.21140 (to be verified on MSRC)
- Microsoft 365 Apps for Enterprise: Unknown; see the MSRC advisory and https://aka.ms/OfficeSecurityReleases
- Office Online Server: Unknown; to be verified on MSRC
- Fix shipped in the November 2026 Patch Tuesday release.
Workaround
Unknown. No vendor workaround identified. Apply the November 2026 Office security update.
Exploitation
- No public proof of concept or in-the-wild exploitation known at publication.
- Microsoft's temporal metrics state Exploit Code Maturity Unproven (E:U) and Report Confidence Confirmed (RC:C).
- NVD status at publication: Awaiting Analysis.
Our recommendation
- Patch Microsoft 365 Apps, Office LTSC and Office for Mac on all Windows and Mac endpoints in the November 2026 update cycle (priority: high).
- Prioritise users who regularly open external spreadsheets.
- Check whether Office Online Server is deployed and, if so, verify its fixed build on MSRC.
- Warn staff about unexpected spreadsheet attachments and downloads.
- Monitor CISA KEV and the NVD entry 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-2026-120788 msrc.microsoft.com
- CVE.org CVE Record: CVE-2026-120788 www.cve.org
- Microsoft November 2026 Patch Tuesday (Cybersecurity News) cybersecuritynews.com
- Strix AI: CVE-2026-120788 (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, 21:32.
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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