Mattermost Agents plugin: Path traversal allows plugin replacement via crafted post
Summary
The Agents plugin of Mattermost Server fails to validate the target post ID in its mention reminder component. An authenticated user who can post in a channel visible to a system administrator can send a crafted post with a forged mention reminder. If the administrator clicks it, the administrator's browser sends an unintended API request that replaces an installed plugin, which can lead to code execution on the server.
Affected
- Mattermost 11.7.0 to 11.7.10
- Mattermost 11.8.0 to 11.8.5
- Mattermost 11.9.0 to 11.9.1
- Only where the Agents plugin is installed
- Versions 11.10.x: to be checked against MMSA-2026-00742
Fixed in
- Mattermost 11.7.11 (per CNA; not yet confirmed by vendor advisory)
- Mattermost 11.8.6 (per CNA; not yet confirmed by vendor advisory)
- Mattermost 11.9.2 (per CNA; not yet confirmed by vendor advisory)
- Mattermost 11.10.0 (per CNA; not yet confirmed by vendor advisory)
Workaround
- No vendor workaround known.
- Disable or remove the Agents plugin if it is not used.
- Restrict who can post in channels visible to administrators.
Exploitation
- Not known to be exploited.
- Not listed in the CISA KEV catalog.
- No public proof of concept known.
- CISA SSVC: Automatable: no; Technical Impact: total.
Our recommendation
- Check whether the Agents plugin is installed on each Mattermost instance.
- Update to the fixed version once the vendor advisory MMSA-2026-00742 confirms it.
- If the plugin is not used, disable or remove it.
- Review the installed plugin list for unexpected changes.
- Tell administrators not to click unexpected mention reminders or unfamiliar posts.
- Recheck the CISA KEV status and the CWE in NVD, as the CVE is new.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Mattermost Security Updates mattermost.com
- Strix CVE-2026-93851 www.strix.ai
- VulDB CVE-2026-93851 vuldb.com
- Mattermost v11 Changelog docs.mattermost.com
- Mattermost Agents plugin (Go package) pkg.go.dev
- The Hacker Wire CVE-2026-93851 www.thehackerwire.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 1 Nov 2026, 21:12.
Original description (NVD)
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Agents plugin's mention reminder component, which allows an authenticated user who can post in a channel visible to a system administrator to cause the administrator's browser to send an unintended API request, resulting in replacement of an installed plugin and code execution on the server, via a crafted post containing a forged mention reminder that the administrator clicks. Mattermost Advisory ID: MMSA-2026-00742
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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