Mattermost: community verdicts
6 notable / known-exploited Mattermost CVEs the community has triaged.
- CVE-2026-8823LOW 3.8EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669
- CVE-2026-9162MED 4.3EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to invalidate cached authentication state for active WebSocket connections during global session revocation, which allows a user with an existing WebSocket connection to remain authenticated and continue receiving real-time events until the cached session expires or the client reconnects.. Mattermost Advisory ID: MMSA-2026-00664
- CVE-2026-8074LOW 3.8EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to enforce bot-specific permission checks on the user active status endpoint, which allows a User Manager with user management write access but no Integrations access to deactivate bot accounts via the PUT /api/v4/users/{id}/active API endpoint.. Mattermost Advisory ID: MMSA-2026-00667
- CVE-2026-6673MED 6.4EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret and disrupt the Jira integration via POST to /ac/installed during the pending-install window.. Mattermost Advisory ID: MMSA-2026-00654
- CVE-2026-5139MED 5.4EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644
- CVE-2026-6062MED 6.4EPSS 0%
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 Fail to validate channel ownership of an existing subscription before applying edits which allows an authenticated attacker to hijack subscriptions from channels they have no access to via a crafted PUT request to the subscription edit endpoint.. Mattermost Advisory ID: MMSA-2026-00650