Microsoft Office Excel: Remote Code Execution via heap-based buffer overflow
Summary
Microsoft Office Excel in Microsoft 365 Apps, Office LTSC, Office for Mac and Office Online Server contains a heap-based buffer overflow (CWE-122). An unauthenticated remote attacker can execute code if a user opens a crafted Excel file, for example an email attachment or a downloaded file. Microsoft and NVD rate the flaw High (CVSS 8.8). No exploitation in the wild is known.
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (see Microsoft advisory)
- Office LTSC 2021 (Windows): 16.0.1 to < 16.0.14334.20974
- Office LTSC 2024 (Windows): 16.0.0 to < 16.0.17932.21056
- Office 365 for Mac: 1.0.0 to < 16.114.26101123
- Office LTSC for Mac 2021 and 2024: 16.0.0 and later, fixed build not yet confirmed
- Office Online Server (self-hosted): 16.0.0.0 to < 16.0.10417.20228
Fixed in
- Microsoft 365 Apps: October 13, 2026 Office security update (exact build: Unknown, check https://aka.ms/OfficeSecurityReleases)
- Office LTSC 2021: 16.0.14334.20974
- Office LTSC 2024: 16.0.17932.21056
- Office 365 for Mac: 16.114.26101123
- Office LTSC for Mac 2021 and 2024: Unknown
- Office Online Server: 16.0.10417.20228 (KB5002928)
Workaround
- No official workaround beyond patching found.
- Block or tightly restrict downloading and opening Excel files from untrusted sources (interim control, especially for Mac LTSC until a fix is released).
Exploitation
- No exploitation in the wild found; not listed in CISA KEV.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public exploit found. VulDB describes the issue differently (CWE-94), which conflicts with the Microsoft and NVD data.
Our recommendation
- Deploy the October 2026 Office security update to all Microsoft 365 Apps and LTSC clients and verify the build against the MSRC advisory.
- Patch self-hosted Office Online Server to 16.0.10417.20228 or later.
- For Mac LTSC, restrict handling of Excel files from untrusted sources until Microsoft releases a fix.
- Warn users about unsolicited Excel attachments and check the email gateway.
- Monitor CISA KEV and vendor updates.
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-2026-97763 msrc.microsoft.com
- Microsoft Office Online Server hotfix KB5002928 support.microsoft.com
- Microsoft 365 Apps security updates (release notes) learn.microsoft.com
- Vulners CVE record CVE-2026-97763 vulners.com
- Strix CVE summary CVE-2026-97763 www.strix.ai
- OpenCVE CVE-2026-97763 app.opencve.io
- VulDB entry 419716 vuldb.com
- NVD CVMAP report 21935 nvd.nist.gov
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, 17:23.
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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