---
id: CVE-2026-6046
aliases:
  - GHSA-3vmp-whvv-5v9v
  - GO-2026-6279
title: >-
  Mattermost doesn't validate that a username returned during bot registration
  belongs to a bot account
summary: >-
  Mattermost doesn't validate that a username returned during bot registration
  belongs to a bot account
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N'
vendor: mattermost
product: github.com/mattermost/mattermost-server
ecosystem: go
affected:
  - 'github.com/mattermost/mattermost-server >= 11.6.0, < 11.6.1'
  - 'github.com/mattermost/mattermost-server >= 11.5.0, < 11.5.5'
  - 'github.com/mattermost/mattermost-server >= 10.11.0, < 10.11.17'
  - >-
    github.com/mattermost/mattermost/server/v8 >=
    8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260428151657-c79c3831061a
patched:
  - github.com/mattermost/mattermost-server 11.6.1
  - github.com/mattermost/mattermost-server 11.5.5
  - github.com/mattermost/mattermost-server 10.11.17
  - github.com/mattermost/mattermost/server/v8 8.0.0-20260428151657-c79c3831061a
published: '2026-06-12'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:55.370444496Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-3vmp-whvv-5v9v'
references:
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-6046'
  - url: 'https://github.com/mattermost/mattermost/pull/36320'
  - url: 'https://github.com/mattermost/mattermost/pull/36318'
  - url: 'https://github.com/mattermost/mattermost/pull/36317'
  - url: 'https://github.com/mattermost/mattermost/pull/36305'
  - url: 'https://github.com/mattermost/mattermost/pull/36064'
  - url: >-
      https://github.com/mattermost/mattermost/commit/f706d1f01e6dfe62cab86c1d257f237daa78106a
  - url: >-
      https://github.com/mattermost/mattermost/commit/c79c3831061a0880c0962c7d567c9e24dd35f44c
  - url: >-
      https://github.com/mattermost/mattermost/commit/aba9339a24d4b287edd77377c19901d6e341bb96
  - url: >-
      https://github.com/mattermost/mattermost/commit/98f9778cec1e7f3d97b3d4692fb91f8e7b659972
  - url: >-
      https://github.com/mattermost/mattermost/commit/3be10297c14d272f273d747af70728f9d03c60ec
  - url: 'https://github.com/mattermost/mattermost/releases/tag/v10.11.16'
  - url: 'https://github.com/mattermost/mattermost/releases/tag/v11.5.5'
  - url: 'https://github.com/mattermost/mattermost/releases/tag/v11.6.2'
  - url: 'https://github.com/mattermost/mattermost/releases/tag/v11.7.0'
  - url: 'https://mattermost.com/security-updates'
  - url: 'https://github.com/mattermost/mattermost'
tags:
  - osv
  - go
epss: 0.0019
epssPercentile: 0.08927
ingestedAt: '2026-08-25T19:26:22.826Z'
---

## Overview

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username. Mattermost Advisory ID: MMSA-2026-00649

## Affected packages

- `github.com/mattermost/mattermost-server >= 11.6.0, < 11.6.1`
- `github.com/mattermost/mattermost-server >= 11.5.0, < 11.5.5`
- `github.com/mattermost/mattermost-server >= 10.11.0, < 10.11.17`
- `github.com/mattermost/mattermost/server/v8 >= 8.0.0-20250731163400-5b955468ea1e, < 8.0.0-20260428151657-c79c3831061a`

## Remediation

Upgrade to a patched release:

- `github.com/mattermost/mattermost-server 11.6.1`
- `github.com/mattermost/mattermost-server 11.5.5`
- `github.com/mattermost/mattermost-server 10.11.17`
- `github.com/mattermost/mattermost/server/v8 8.0.0-20260428151657-c79c3831061a`