Microsoft Office Excel: Heap-based buffer overflow allows remote code execution
Summary
A heap-based buffer overflow in Microsoft Office Excel, shipped in Microsoft 365 Apps, Office LTSC and Office for Mac editions, 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 the internet. Microsoft rates the flaw Critical, the CVSS base score is 8.8 (High), and no exploitation in the wild or public proof of concept has been reported.
Affected
- Microsoft 365 Apps for Enterprise (32- and 64-bit)
- Office 365 for Mac: versions before 16.114.26101123
- Office LTSC 2021: versions before 16.0.14334.20974
- Office LTSC 2024: versions before 16.0.17932.21056
- Office LTSC for Mac 2021 and 2024: versions before 16.114.26101123 (fixed builds unknown)
- Office Online Server: versions before 16.0.10417.20228
Fixed in
- October 2026 security update for all listed products
- Exact fixed builds for Microsoft 365 Apps for Enterprise: Unknown (check the MSRC advisory)
- Fixed builds for Office LTSC for Mac 2021 and 2024: Unknown (update may not yet be available)
Workaround
- No official workaround identified.
- Keep Protected View enabled and do not open Excel files from untrusted sources.
Exploitation
- In the wild: none known.
- Public proof of concept: none known; MSRC marks exploit code maturity as Unproven.
- CISA SSVC: exploitation none, automatable no.
Our recommendation
- Install the October 2026 security update on all affected Office installations, including Office Online Server if used.
- For Mac LTSC editions without an update yet, keep Protected View enabled and monitor for the update.
- Check the MSRC advisory for exact fixed builds before rollout.
- Keep Protected View enabled and warn users about unsolicited Excel attachments.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Critical
- 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 Response Center: CVE-2026-97765 msrc.microsoft.com
- MSRC advisory CVE-2026-97765 msrc.microsoft.com
- OpenCVE: CVE-2026-97765 app.opencve.io
- Vulners: CVE-2026-97765 vulners.com
- Action1: Patch Tuesday October 2026 www.action1.com
- Talos: Microsoft Patch Tuesday October 2026 blog.talosintelligence.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, 17:24.
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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