CVE-2026-93851: Path traversal in Mattermost Agents plugin mention reminder allows plugin replacement via crafted post
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
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.10.0 - Upgrade
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Mattermostto a version that resolves this vulnerability.Fixed in 11.9.2 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.8.6 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.7.11
Event History
Frequently Asked Questions
Who is exposed to this issue?
Instances in the listed Mattermost 11.9.x, 11.8.x, and 11.7.x ranges are exposed when the Agents plugin mention reminder component is present and a system administrator can view a channel where a lower-privileged authenticated user can post.
What does an attacker need to exploit it?
The attacker needs an authenticated Mattermost account with permission to post in a channel visible to a system administrator. They must craft a post containing a forged mention reminder and induce the administrator to click it.
What is the impact if exploitation succeeds?
The administrator's browser can be caused to send an unintended API request that replaces an installed plugin. This can result in code execution on the Mattermost server.