CVE-2026-9693: Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite
Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.9.0 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 10.11.21 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.7.6
Event History
Frequently Asked Questions
What is the severity of CVE-2026-9693?
CVE-2026-9693 has a severity score of 3.5, classified as low.
How do I fix CVE-2026-9693?
To fix CVE-2026-9693, update Mattermost to version 10.11.21 or 11.7.6 or later.
What are the affected versions of Mattermost for CVE-2026-9693?
The affected versions are Mattermost 10.11.x up to 10.11.20 and 11.7.x up to 11.7.5.
What does CVE-2026-9693 expose?
CVE-2026-9693 exposes private channel thread metadata and root post content to previously removed users upon re-invitation.
What conditions are necessary for CVE-2026-9693 to be exploited?
CVE-2026-9693 can be exploited if a user is removed from a team and later re-invited, without proper thread membership record removal.