CVE-2026-9693 PUBLISHED

Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite

Assigner: Mattermost
Reserved: 27.05.2026 Published: 17.08.2026 Updated: 17.08.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N
CVSS Score: 3.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	Low
Privileges Required	Low	Integrity Impact	None
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 10.11.0 to 10.11.20 (incl.) affected from 11.7.0 to 11.7.5 (incl.) Version 11.9.0 is unaffected Version 10.11.21 is unaffected Version 11.7.6 is unaffected

Solutions

Update Mattermost to versions 11.9.0, 10.11.21, 11.7.6 or higher.

Credits

kiwi_71 finder

References

MMSA-2026-00682

Problem Types

CWE-459: Incomplete Cleanup CWE