Microsoft Office Excel: Remote code execution due to use-after-free
Summary
A use-after-free vulnerability (CWE-416) in Microsoft Office Excel, part of Microsoft 365 Apps and Office, allows an unauthorized attacker to execute code over a network. The CVSS vector indicates that user interaction is required, for example opening a crafted file, so email and file sharing are the main exposure. Exploitation is not confirmed and the CVE is not listed in CISA KEV. The CVSS base score is 8.8 (High).
Affected
- Microsoft 365 Apps for Enterprise: 16.0.1 up to the fixed build (exact fixed build unknown)
- Microsoft Office 365 for Mac: 1.0.0 to before 16.114.26101123
- Microsoft Office LTSC 2021: 16.0.1 to before 16.0.14334.20974
- Microsoft Office LTSC 2024: 16.0.0 to before 16.0.17932.21056
- Microsoft Office LTSC for Mac 2021 and 2024: 16.0.0 or 16.0.1 to before 16.114.26101123
- Microsoft Office Online Server: 16.0.0.0 to before 16.0.10417.20228
Fixed in
- Microsoft 365 Apps for Enterprise: Unknown
- Microsoft Office 365 for Mac: 16.114.26101123 (per CVE record, not verified on MSRC)
- Microsoft Office LTSC 2021: 16.0.14334.20974 (per CVE record, not verified on MSRC)
- Microsoft Office LTSC 2024: 16.0.17932.21056 (per CVE record, not verified on MSRC)
- Microsoft Office LTSC for Mac 2021 and 2024: 16.114.26101123 (per CVE record, not verified on MSRC)
- Microsoft Office Online Server: 16.0.10417.20228 (per CVE record, not verified on MSRC)
Workaround
- No Microsoft workaround was confirmed. Installing the security update is the expected remedy.
- Restrict Office files from unknown external senders as general practice (not specific to this CVE).
Exploitation
- Not confirmed as exploited in the wild for this CVE.
- Not listed in CISA KEV at the time of research.
- EPSS score 0.00788 (low).
- No public proof of concept found; this does not prove that none exists.
- CISA SSVC: exploitation none, automatable no, technical impact total.
Our recommendation
- Install the October 2026 security updates for Microsoft 365 Apps and Office on all Excel clients as a priority.
- Confirm exact fixed builds on the MSRC page before relying on version numbers.
- Check whether Office Online Server is in use and internet-facing, and patch it if so.
- Monitor for suspicious Excel attachments and re-check the CISA KEV catalogue 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 Response Center: CVE-2026-100212 msrc.microsoft.com
- NVD record via vulners.com vulners.com
- Microsoft 365 Apps security updates learn.microsoft.com
- Release notes for Office for Mac learn.microsoft.com
- Strix: CVE-2026-100212 (third-party, unverified) www.strix.ai
- Talos: Microsoft Patch Tuesday October 2026 blog.talosintelligence.com
- Qualys: Microsoft Patch Tuesday October 2026 review blog.qualys.com
- GitHub issue: CVE-2026-100212 KEV status 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, 19:37.
Original description (NVD)
Use after free 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.