---
id: "CVE-2026-93851"
kind: "vulnerability"
aliases: ["CVE-2026-93851"]
title: "Mattermost: forged mention reminder lets a post trigger plugin replacement and server code execution"
severity: "high"
cvss: 8.0
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["agents-plugin", "mattermost", "package", "plugins", "self-hosted"]
not_affected_if: ["default-config"]
published_at: "2026-10-28T22:17:17+00:00"
first_seen_at: "2026-10-28T22:35:35+00:00"
updated_at: "2026-10-28T22:36:42+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93851", "first_seen_at": "2026-10-28T22:35:35+00:00"}]
---

# Mattermost: forged mention reminder lets a post trigger plugin replacement and server code execution

Mattermost's Agents plugin does not validate the target post ID in its mention reminder component. A user who can post in a channel an administrator can see can plant a crafted post that, when the administrator clicks it, makes the administrator's browser replace an installed plugin, which leads to code execution on the server.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the Mattermost server version with `mattermost version` and compare it to the affected lines: 11.9.x up to 11.9.1, 11.8.x up to 11.8.5, 11.7.x up to 11.7.10.
- Check whether the Agents plugin is installed and its version in System Console > Plugins > Plugin Management.

## Fix

- Upgrade Mattermost to a release that includes the MMSA-2026-00742 fix: a fixed build for 11.9.x, 11.8.x or 11.7.x beyond the listed affected versions (exact fixed version unknown from the sources).
- Update the Agents plugin to the fixed release that ships with that server build (exact version unknown from the sources).

## Timeline

- 2026-10-28T22:35:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-93851

## From the sources

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

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_