Microsoft Office Excel: Stack-based buffer overflow allows remote code execution
Summary
Microsoft Excel, part of Microsoft 365 Apps and Office, contains a stack-based buffer overflow (CWE-121). An attacker can execute code on a vulnerable system over the network without authentication. According to a third-party source, the flaw is triggered when a user opens a malicious spreadsheet, so phishing with attachments is the main risk.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (exact build unknown)
- Office 365 for Mac: before 16.114.26101123
- Office LTSC 2021: 16.0.1 up to 16.0.14334.20974
- Office LTSC 2024: 16.0.0 up to 16.0.17932.21056
- Office LTSC for Mac 2021: before 16.114.26101123
- Office LTSC for Mac 2024: before 16.114.26101123
- Office Online Server: 16.0.0.0 up to 16.0.10417.20228
Fixed in
- Microsoft's security updates of October 13, 2026 (Windows and Office channels)
- Office LTSC 2021: 16.0.14334.20974 (per third-party mirror, verify on MSRC)
- Office LTSC 2024: 16.0.17932.21056 (per third-party mirror, verify on MSRC)
- Office Online Server: 16.0.10417.20228 (per third-party mirror, verify on MSRC)
- Microsoft 365 Apps and Office for Mac: Excel update listed for October 14, 2026; fixed build unknown
Workaround
Unknown. No vendor workaround found.
- Until patched, do not open unsolicited spreadsheets, especially attachments from unknown senders.
- Keep Protected View enabled in Office.
Exploitation
- No evidence of exploitation in the wild found; not listed in the CISA KEV catalog.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public proof of concept found in non-exhaustive searches.
Our recommendation
- Install the October 2026 Microsoft 365 and Office security updates on all desktops and servers without delay.
- Enable automatic updates for Microsoft Office.
- Check whether Office Online Server is in use and exposed to the internet; patch it first if so.
- Remind staff to be cautious with unexpected spreadsheet attachments and links.
- Monitor email gateways for suspicious Excel attachments.
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-2026-97770 msrc.microsoft.com
- OpenCVE: CVE-2026-97770 app.opencve.io
- Microsoft Support: KB5002928 Office Online Server support.microsoft.com
- Microsoft Office for Mac release notes learn.microsoft.com
- VulDB: vuln 419681 vuldb.com
- Vulners: CVE-2026-97770 vulners.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, 17:27.
Original description (NVD)
Stack-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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