Inadequate Thread Membership Management in Mattermost by Mattermost Inc.
CVE-2026-9693

3.5LOW

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
17 August 2026

What is CVE-2026-9693?

The Mattermost platform has a vulnerability that arises when a user leaves or is removed from a team. It fails to clean up thread membership records, enabling these users to regain access to private channel content and metadata through the team threads API if they are later re-invited. This oversight can lead to unauthorized visibility of sensitive information, thereby compromising the security posture of teams using the platform.

Affected Version(s)

Mattermost 10.11.0 <= 10.11.20

Mattermost 11.7.0 <= 11.7.5

Mattermost 11.9.0

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
3.5
Severity:
LOW
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

kiwi_71
.