Microsoft Office Excel: Remote Code Execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over the network. Exploitation requires that a user opens a crafted Excel file, for example one received by email or downloaded. Microsoft 365 Apps, Office LTSC, Office for Mac and Office Online Server are listed as affected.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 before the update release at https://aka.ms/OfficeSecurityReleases
- Microsoft Office 365 for Mac: 1.0.0 to before 16.115.26110837
- Microsoft Office LTSC 2021: 16.0.1 to before 16.0.14334.21048
- Microsoft Office LTSC 2024: 16.0.0 to before 16.0.17932.21140
- Microsoft Office LTSC for Mac 2021: 16.0.1 to before 16.115.26110837
- Microsoft Office LTSC for Mac 2024: 16.0.0 to before 16.115.26110837
- Microsoft Office Online Server: 16.0.0.0 to before 16.0.10417.20236 (to be checked against MSRC)
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown (fixed build not stated in the sources; see MSRC)
- Microsoft Office 365 for Mac: 16.115.26110837
- Microsoft Office LTSC 2021: 16.0.14334.21048
- Microsoft Office LTSC 2024: 16.0.17932.21140 (from secondary sources, to be verified)
- Microsoft Office LTSC for Mac 2021 and 2024: 16.115.26110837
- Microsoft Office Online Server: 16.0.10417.20236
Workaround
Unknown. No workaround is described in the sources.
- Keep Office on the update channel
- Block or sandbox untrusted and macro-free Excel attachments
- Restrict where Excel files are accepted from (email, downloads)
Exploitation
- No exploitation known at publication.
- No public proof of concept and no CISA KEV entry found.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- CVSS exploit code maturity: unproven (E:U).
Our recommendation
- Patch Microsoft 365 Apps and LTSC Office clients as a priority, ideally via the current monthly update.
- Check whether Office Online Server or a SharePoint on-premises farm is deployed and patch it if so.
- Verify the affected and fixed versions against the MSRC advisory before rollout.
- Watch for exploitation reports and keep users cautious with unexpected Excel files.
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-2026-118299 msrc.microsoft.com
- CVE Record CVE-2026-118299 (CVE.org) www.cve.org
- Strix.ai: CVE-2026-118299 www.strix.ai
- Threatint: CVE-2026-118299 cve.threatint.com
- SharePoint security fixes November 2026 PU (Stefan Gossner) blog.stefan-gossner.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, 22:04.
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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