Microsoft Excel: Heap-based buffer overflow enabling remote code execution
Summary
A heap-based buffer overflow in Microsoft Excel, part of Microsoft Office and Microsoft 365 Apps, allows an unauthorized attacker to execute code over a network. Exploitation requires that a user opens a malicious file, typically an email attachment or a file downloaded from a link. No privileges are needed, and no exploitation has been reported so far.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 to before the update listed at 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 and 2024: 16.0.1 to before 16.115.26110837
- Office Online Server: 16.0.0.0 to before 16.0.10417.20236
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown from the sources; check the Microsoft advisory and the update link aka.ms/OfficeSecurityReleases
- Office 365 for Mac and Office LTSC for Mac: 16.115.26110837 or later
- Office LTSC 2021: 16.0.14334.21048 or later
- Office LTSC 2024: 16.0.17932.21140 or later
- Office Online Server: 16.0.10417.20236 or later
Workaround
Unknown. No documented workaround could be verified. Keep Protected View and the blocking of internet-sourced files enabled as defense in depth.
Exploitation
- No exploitation has been reported. CISA SSVC lists exploitation as none.
- The exploit code maturity in the CVE record is unproven (E:U).
- No public proof-of-concept found.
- No CISA KEV entry found.
- The actively exploited November 2026 Outlook flaw is CVE-2026-124194, not this CVE.
Our recommendation
- Inventory Excel and Office versions and update channels, including Mac and LTSC systems.
- Install the November 2026 updates and confirm the installed builds against the Microsoft Security Update Guide.
- Check whether LTSC for Mac updates are delayed and verify them manually.
- Keep Office file-open protections enabled and train staff to be cautious with unexpected Excel attachments and links.
- Monitor for suspicious Office child processes and unexpected file downloads.
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 Update Guide: CVE-2026-118302 msrc.microsoft.com
- CVE Record CVE-2026-118302 www.cve.org
- Strix: CVE-2026-118302 www.strix.ai
- Tenable: Microsoft November 2026 Patch Tuesday www.tenable.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, 22:05.
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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