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. The attack requires a user to interact, for example by opening a crafted Excel file received by email or download. Microsoft rates the vulnerability as High (CVSS 3.1: 8.8), and CISA SSVC rates the technical impact as total.
Affected
- Microsoft 365 Apps for Enterprise (version range listed in the CVE record only as a link to Microsoft's release information)
- Microsoft Office 365 for Mac: 1.0.0 up to 16.114.26101123 (excluded)
- Microsoft Office LTSC 2021: 16.0.1 up to 16.0.14334.20974 (excluded)
- Microsoft Office LTSC 2024: 16.0.0 up to 16.0.17932.21056 (excluded)
- Microsoft Office LTSC for Mac 2021: 16.0.1 up to 16.114.26101123 (excluded)
- Microsoft Office LTSC for Mac 2024: 16.0.0 up to 16.114.26101123 (excluded)
- Microsoft Office Online Server: 16.0.0.0 up to 16.0.10417.20228 (excluded)
Fixed in
- Microsoft Office Online Server: 16.0.10417.20228 (Microsoft KB5002928)
- Other products: fixed builds not confirmed in the sources; check the Microsoft Security Update Guide entry.
Workaround
No vendor workaround known. Installing the security update is the documented remedy.
Exploitation
- No public exploit code found.
- CISA SSVC in the CVE record: Exploitation none, Automatable no.
- Not listed in the CISA KEV catalog at the time of research.
- Talos reports one vulnerability from the October 2026 Patch Tuesday as exploited in the wild, but does not name this CVE.
Our recommendation
- Install the October 2026 Office security updates on all affected Excel installations as part of the normal patch cycle, and prioritize user workstations that process external files.
- Check the Microsoft Security Update Guide entry for the fixed build of your Microsoft 365 Apps channel.
- Replace or upgrade Office LTSC 2021 systems, because support for that version ended on October 13, 2026.
- Keep email filtering and Protected View enabled, and handle unsolicited spreadsheets with caution.
- Check whether Office Online Server runs on-premises and whether it is reachable from the internet.
- Monitor the CISA KEV catalog and the Microsoft advisory for changes in exploitation status.
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-2026-97766 msrc.microsoft.com
- OpenCVE: CVE-2026-97766 app.opencve.io
- Microsoft Support: Office Online Server update KB5002928 support.microsoft.com
- Microsoft Learn: Office security updates for Microsoft 365 Apps learn.microsoft.com
- Microsoft Learn: Release notes for Office for Mac learn.microsoft.com
- Strix.ai: CVE-2026-97766 www.strix.ai
- Talos: Microsoft Patch Tuesday for 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, 17:25.
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.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.