Microsoft Office Click-to-Run: Elevation of privilege via use-after-free
Summary
A use-after-free flaw in the Microsoft Office Click-to-Run component allows a locally authenticated attacker with low privileges to elevate their privileges on the system. Exploitation requires local access and a valid low-privilege account or foothold, and no user interaction. The flaw is not internet-facing, but it is a risk on shared or multi-user systems.
Affected
- Microsoft 365 Apps for Enterprise (16.0.1 to the fixed build listed on the Microsoft release page)
- Microsoft Office LTSC 2021 (16.0.1 to below 16.0.14334.20974)
- Microsoft Office LTSC 2024 (16.0.0 to below 16.0.17932.21056)
Fixed in
- Microsoft Office LTSC 2021: 16.0.14334.20974 or later
- Microsoft Office LTSC 2024: 16.0.17932.21056 or later
- Microsoft 365 Apps for Enterprise: Unknown. Check https://aka.ms/OfficeSecurityReleases and the MSRC page for the fixed build.
Workaround
Unknown.
Exploitation
- Microsoft rated the vulnerability as not publicly disclosed and not exploited at original publication.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- Not listed in the CISA KEV catalogue at the time of research.
- No public proof of concept found; this does not prove none exists.
Our recommendation
- Install the Click-to-Run update on all Microsoft 365 Apps and Office LTSC 2021/2024 clients, starting with shared PCs, terminal servers and RDS hosts.
- Confirm the fixed Microsoft 365 Apps build on the MSRC page before rollout.
- Limit local accounts on multi-user systems and monitor for unexpected privilege changes.
- Recheck CISA KEV and public PoC sources for changes.
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-2026-88109 msrc.microsoft.com
- Vulners CVELIST record CVE-2026-88109 vulners.com
- OpenCVE CVE-2026-88109 app.opencve.io
- OffSeq Radar: CVE-2026-88109 radar.offseq.com
- Strix AI: CVE-2026-88109 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 2 Nov 2026, 01:25.
Original description (NVD)
Use after free in Microsoft Office Click-To-Run allows an authorized attacker to elevate privileges locally.
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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