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 a network. Exploitation requires that a user opens a manipulated Excel file, for example one received by email or downloaded from a shared drive. Successful exploitation can lead to full compromise of confidentiality, integrity and availability on the affected system.
Affected
- Microsoft 365 Apps for Enterprise (16.0.1 and later, exact builds per Microsoft release page)
- Microsoft Office 365 for Mac (1.0.0 before 16.115.26110837)
- Office LTSC 2021 (16.0.1 before 16.0.14334.21048)
- Office LTSC 2024 (16.0.0 before 16.0.17932.21140; version per third-party mirror, to be verified)
- Office LTSC for Mac 2021 and 2024 (before 16.115.26110837; per third-party mirror, to be verified)
- Office Online Server (before 16.0.10417.20236; per third-party mirror, to be verified)
Fixed in
- Microsoft 365 Apps for Enterprise: current builds via https://aka.ms/OfficeSecurityReleases (exact build unknown)
- Office 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 (to be verified)
- Office Online Server: 16.0.10417.20236 or later (to be verified)
Workaround
Unknown. No vendor workaround was found; apply the security update.
Exploitation
- No source confirms exploitation in the wild.
- The CVSS vector carries E:U (Unproven exploit maturity).
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- No public proof of concept was found; status is unknown because the NVD entry is still awaiting analysis.
Our recommendation
- Verify affected and fixed builds on the MSRC advisory, as the version data in the sources is partly inconsistent.
- Install the November 2026 Office security updates on all endpoints, including LTSC and Office for Mac installations that often need manual updates.
- Check the build numbers on each endpoint.
- Train users not to open Excel files from unknown senders or untrusted shared drives.
- Monitor NVD and CISA KEV for changes in exploitation status.
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
- MSRC Security Update Guide: CVE-2026-118298 msrc.microsoft.com
- CVE.org CVE Record: CVE-2026-118298 www.cve.org
- Strix: CVE-2026-118298 www.strix.ai
- threatint: CVE-2026-118298 cve.threatint.com
- Stefan Gossner blog: November 2026 SharePoint and Office security fixes 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, 22:03.
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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