Microsoft Office Excel: Remote code execution through integer underflow
Summary
A integer underflow (CWE-191) in Microsoft Office Excel allows an unauthorized attacker to execute code. Exploitation requires that a victim opens a crafted file, for example an email attachment or a downloaded spreadsheet, so user interaction is needed (CVSS 8.8, UI:R). Successful exploitation can lead to a high impact on confidentiality, integrity and availability on the affected computer.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (see MSRC)
- 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 (secondary source, confirm on MSRC)
- Microsoft Office LTSC for Mac 2021 and 2024: before 16.115.26110837 (secondary source, confirm on MSRC)
- Microsoft Office Online Server: 16.0.0.0 before 16.0.10417.20236 (secondary source, confirm on MSRC)
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown. See the MSRC advisory.
- Office 365 for Mac: 16.115.26110837
- Office LTSC 2021: 16.0.14334.21048
- Office LTSC 2024: 16.0.17932.21140 (secondary source)
- Office LTSC for Mac 2021 and 2024: 16.115.26110837 (secondary source)
- Office Online Server: 16.0.10417.20236 (secondary source)
Workaround
- No vendor-published workaround known.
- Until patched: do not open unsolicited spreadsheets from email or downloads, keep Protected View enabled, and block macros and unneeded file types via group policy.
Exploitation
- No evidence of exploitation in the wild found.
- CISA SSVC: exploitation none, not automatable, total technical impact.
- CVSS exploit maturity is unproven (E:U).
- No public proof of concept found.
Our recommendation
- Patch Microsoft 365 Apps, Office LTSC and Office for Mac through the normal Microsoft update channels, and verify the build numbers on MSRC first.
- Patch Office in the same window as the other Excel fixes of the November 2026 release.
- Prioritize Excel users who receive external files by email or download.
- Brief staff not to open unexpected spreadsheets and monitor for public exploit code, as the CVSS rating is currently unproven.
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
- CVE Record CVE-2026-118712 www.cve.org
- Microsoft Security Update Guide CVE-2026-118712 msrc.microsoft.com
- Strix CVE-2026-118712 (secondary build data) www.strix.ai
- Cybersecurity News: Microsoft November 2026 Patch Tuesday 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, 21:53.
Original description (NVD)
Integer underflow (wrap or wraparound) 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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