Microsoft Office Access: Remote code execution via heap-based buffer overflow
Summary
A heap-based buffer overflow in Microsoft Office Access, part of Microsoft 365 Apps, Office LTSC 2021 and Office LTSC 2024, allows an unauthorized attacker to execute code over a network. The attack requires a victim to open a crafted file or follow a crafted link, so user interaction is needed. Successful exploitation could lead to full compromise of confidentiality, integrity and availability on the affected system.
Affected
- Microsoft 365 Apps for Enterprise (16.0.1 up to the fixed build, exact build to be confirmed by Microsoft)
- Microsoft Office LTSC 2021: versions 16.0.1 to before 16.0.14334.20974 (to be verified)
- Microsoft Office LTSC 2024: versions 16.0.0 to before 16.0.17932.21056 (to be verified)
- CVSS 3.1 base score 8.8 (NVD/CNA); VulDB lists 5.5 and CWE-120
Fixed in
- October 2026 Microsoft Office security update for Microsoft 365 Apps, Office LTSC 2021 and Office LTSC 2024
- Exact fixed build numbers per channel: Unknown. Confirm at https://aka.ms/OfficeSecurityReleases and the MSRC advisory.
Workaround
- Unknown. No vendor workaround was found in the sources.
- Until patched: restrict or block untrusted Access files and links, and keep Protected View enabled.
Exploitation
- CISA SSVC: Exploitation none, automatable no, technical impact total.
- Not listed in CISA KEV as of the sources checked.
- EPSS about 0.007 (low predicted exploitation probability).
- No public proof of concept found; this does not prove none exists.
- No reports of exploitation in the wild found.
Our recommendation
- Deploy the October 2026 Office update to all clients with Access installed, prioritising mail and file-handling roles.
- Confirm the fixed builds on the MSRC advisory and aka.ms/OfficeSecurityReleases.
- Check Office build numbers in your inventory to find unpatched endpoints.
- Patch related CVEs released the same day in the same cycle.
- Re-check CISA KEV and public exploit sources regularly.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-105591 msrc.microsoft.com
- Microsoft 365 Apps security updates learn.microsoft.com
- Office security releases (aka.ms link referenced by MSRC) msrc.microsoft.com
- NVD copy (Vulners) vulners.com
- MS:CVE-2026-105591 (Vulners mirror) vulners.com
- VulDB entry 418022 vuldb.com
- CISA KEV status tracker (GitHub) 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, 19:15.
Original description (NVD)
Heap-based buffer overflow in Microsoft Office Access 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.