Microsoft Office Excel: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Excel allows an unauthenticated attacker to execute code over a network. The attacker needs a user to take an action, such as opening a manipulated spreadsheet. Microsoft rates the CVSS 3.1 base score at 8.8 (High).
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 onward (fixed version not stated in the CNA record)
- Office LTSC 2021: before 16.0.14334.20974
- Office LTSC 2024: before 16.0.17932.21056
- Office 365 for Mac and Office LTSC for Mac 2021/2024: before 16.114.26101123
- Office Online Server: before 16.0.10417.20228 (not verified against MSRC)
Fixed in
- Security updates released on 13 October 2026 for the products listed above.
- Office LTSC 2021: 16.0.14334.20974 or later
- Office LTSC 2024: 16.0.17932.21056 or later
- Office for Mac: 16.114.26101123 or later
- Deploy the newest build available for your channel, as Microsoft reports a paste regression in Excel 16.0.5574.1005 that is fixed in 16.0.5574.1006.
Workaround
Unknown. No workaround documented by Microsoft was found in the available sources.
Exploitation
- CISA SSVC: exploitation none, automatable no, technical impact total.
- Microsoft temporal score: exploit code maturity unproven (E:U).
- No public exploit code or active exploitation was found at the time of writing.
Our recommendation
- Install the October 2026 Microsoft Office security updates on all Excel endpoints.
- Verify the installed build with the version numbers above, especially for Microsoft 365 Apps and Office Online Server.
- Until patched, treat spreadsheets from unknown or untrusted sources with caution and do not enable macros or editing from unexpected emails.
- Monitor for unusual Excel crashes or 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-2026-97777 msrc.microsoft.com
- Vulners: CNA record CVE-2026-97777 vulners.com
- Microsoft 365 Apps security updates learn.microsoft.com
- Microsoft Excel 2016 hotfix KB5002934 support.microsoft.com
- Microsoft Office hotfix index KB5130763 support.microsoft.com
- Microsoft Current Channel release notes learn.microsoft.com
- Strix: CVE-2026-97777 (third-party, unverified) www.strix.ai
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, 17:22.
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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