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. No privileges are required, but a victim must open or process a crafted file, for example a spreadsheet received by email or download. The flaw is rated CVSS 8.8 (High) and Microsoft has released fixes in October 2026.
Affected
- Microsoft 365 Apps for Enterprise (64-bit)
- Office LTSC 2021 (32- and 64-bit) before 16.0.14334.20974
- Office LTSC 2024 (32- and 64-bit) before 16.0.17932.21056
- Office for Mac and Office LTSC for Mac 2021/2024 before 16.114.26101123
- Office Online Server before 16.0.10417.20228
Fixed in
- Office Online Server: 16.0.10417.20228 (KB5002928, October 13, 2026 release)
- Office LTSC 2021: 16.0.14334.20974 (per CVE record; not independently verified)
- Office LTSC 2024: 16.0.17932.21056 (per CVE record; not independently verified)
- Office for Mac and Office LTSC for Mac: 16.114.26101123 (per CVE record and October 14, 2026 release notes)
- Microsoft 365 Apps: Unknown build number; October 2026 update, see MSRC
Workaround
- Unknown. No Microsoft-documented workaround was found.
- General hardening: keep Protected View enabled for files from the internet and email, and block untrusted attachments at the mail gateway.
Exploitation
- Not listed in the CISA KEV catalog.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public proof-of-concept code or in-the-wild exploitation was found. This is a negative search result, not proof that none exists.
Our recommendation
- Install the October 2026 Microsoft 365 and Office updates on all endpoints and verify the installed build.
- Update Office Online Server to 16.0.10417.20228 if it is in use, and check whether it is published to the internet.
- Block or quarantine unsolicited spreadsheet attachments and keep Protected View enabled.
- Monitor endpoints for Excel starting unexpected child processes.
Information from Microsoft (Patch Tuesday October 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)
- KB5002928
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-97751 msrc.microsoft.com
- OpenCVE: CVE-2026-97751 app.opencve.io
- Microsoft Support: KB5002928 (Office Online Server security update) support.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- Release notes for Office for Mac learn.microsoft.com
- Vulners: CVE-2026-97751 vulners.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 31 Oct 2026, 17:36.
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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