Mattermost fails to enforce create_post permission when editing posts

Summary

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to check the create_post channel permission during post edit operations which allows an authenticated attacker with revoked posting privileges to modify their existing posts via direct API requests to the post update and patch endpoints.. Mattermost Advisory ID: MMSA-2026-00627

Timeline

1. May 18, 2026, 6:53 AM UTCCVE published
2. May 18, 2026, 2:34 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. May 18, 2026, 2:35 PM UTCRecord last updated

Affected versions

• Mattermost Mattermost

  From 11.5.0 · through 11.5.1; From 10.11.0 · through 10.11.13; From 11.4.0 · through 11.4.3

• github.com/mattermost/mattermost/server/v8Go

  From 10.11.0 · fixed in 10.11.14

• github.com/mattermost/mattermost/server/v8Go

  From 11.4.0 · fixed in 11.4.4

• github.com/mattermost/mattermost/server/v8Go

  fixed in 8.0.0-20260316171743-090408f09f53

• github.com/mattermost/mattermost/server/v8Go

  From 11.5.0 · fixed in 11.5.2

• github.com/mattermost/mattermost-serverGo

  fixed in 5.3.2-0.20260316171743-090408f09f53

• github.com/mattermost/mattermost-serverGo

  From 10.11.0+incompatible · fixed in 10.11.14+incompatible; From 11.4.0+incompatible · fixed in 11.4.4+incompatible; From 11.5.0+incompatible · fixed in 11.5.2+incompatible

• github.com/mattermost/mattermost-server/v5Go

  All versions

• github.com/mattermost/mattermost-server/v6Go

  All versions

References 1