Microsoft Office Excel: Remote code execution via heap-based buffer overflow
Summary
Microsoft Office Excel contains a heap-based buffer overflow (CWE-122) that allows an unauthenticated attacker to execute code over a network. Exploitation requires that a user opens a crafted spreadsheet, for example one received by email or downloaded from the internet. The vulnerability is rated CVSS 8.8 (High). No exploitation in the wild is known.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (upper bound unclear in vendor data, verify on MSRC)
- Office 365 for Mac: 1.0.0 to below 16.114.26101123
- Office LTSC 2021: 16.0.1 to below 16.0.14334.20974
- Office LTSC 2024: 16.0.0 to below 16.0.17932.21056
- Office LTSC for Mac 2021: 16.0.1 to below 16.114.26101123
- Office LTSC for Mac 2024: 16.0.0 to below 16.114.26101123
- Office Online Server: 16.0.0.0 to below 16.0.10417.20228
Fixed in
- Office LTSC 2021: 16.0.14334.20974 (vendor data, verify on MSRC)
- Office LTSC 2024: 16.0.17932.21056 (vendor data, verify on MSRC)
- Office Online Server: 16.0.10417.20228 (confirmed by Microsoft KB5002928)
- Microsoft 365 Apps and Office for Mac: fixed build unknown, see the MSRC advisory
Workaround
No vendor workaround known. Install the security update.
- Keep Protected View enabled.
- Block macros from internet-sourced files.
- Filter or sandbox spreadsheet attachments in email.
Exploitation
No evidence of exploitation in the wild. CISA SSVC: Exploitation none, Automatable no, Technical Impact total. No public proof-of-concept found. CISA KEV status not verified.
Our recommendation
- Patch Microsoft 365 Apps, Office 2021/2024, Office for Mac and Office Online Server in the normal Patch Tuesday cycle.
- Verify installed build numbers against the MSRC advisory.
- If Office Online Server is deployed on-premises, patch it or take it offline until it is patched.
- Monitor for unusual Excel activity and check the CISA KEV catalog for changes.
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-2026-97773 msrc.microsoft.com
- Microsoft KB5002928: Office Online Server update support.microsoft.com
- Microsoft Office for Mac release notes learn.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- OpenCVE: CVE-2026-97773 app.opencve.io
- Strix: CVE-2026-97773 (third-party mirror) 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, 17:20.
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.