Microsoft Office Excel: Heap-based buffer overflow allows remote code execution
Summary
A heap-based buffer overflow in Microsoft Office Excel, part of Microsoft 365 Apps, Office LTSC and Office for Mac, allows an unauthorized attacker to execute code over a network. Exploitation requires that a user opens or otherwise processes a malicious Excel file, for example one delivered by email or a file share. Office Online Server is also listed as affected. Microsoft rates the issue as Important with a base CVSS score of 8.8.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build referenced by Microsoft (exact build: see MSRC advisory)
- Office LTSC 2021: versions below 16.0.14334.20974
- Office LTSC 2024: versions below 16.0.17932.21056
- Office 365 for Mac: versions below 16.114.26101123
- Office LTSC for Mac 2021 and 2024: fixed build unknown
- Office Online Server: versions below 16.0.10417.20228
Fixed in
- Install the Microsoft Office security update released on October 13, 2026.
- Exact fixed builds for Microsoft 365 Apps and Office for Mac LTSC: see MSRC advisory (partly unverified).
Workaround
- No vendor workaround identified in the sources reviewed. Unknown whether Microsoft lists interim mitigations.
Exploitation
- Not listed in CISA KEV.
- Microsoft exploit code maturity: unproven (E:U).
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public proof-of-concept found. EPSS: unknown.
Our recommendation
- Install the October 13, 2026 Office updates on all clients and on any Office Online Server, using the exact builds from the MSRC advisory.
- Verify that your update channel (Microsoft 365 Apps or LTSC) actually delivers the new build.
- Do not expose Office Online Server to the internet unless required.
- Restrict or sandbox handling of Excel files from untrusted sources and train users on suspicious attachments.
- Monitor for KEV addition or public proof-of-concept code.
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
- MSRC Security Update Guide: CVE-2026-97003 msrc.microsoft.com
- Microsoft Support: Office Online Server hotfix KB5002928 support.microsoft.com
- OpenCVE: CVE-2026-97003 app.opencve.io
- Strix: CVE-2026-97003 www.strix.ai
- Vulners: CVELIST:CVE-2026-97003 vulners.com
- GitHub issue: CVE-2026-97003 tracking github.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, 17:46.
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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