Improper Channel Membership Validation in Mattermost by Mattermost
CVE-2026-20796

3.1LOW

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
13 February 2026

What is CVE-2026-20796?

Mattermost versions 10.11.x up to 10.11.9 have a vulnerability in their handling of channel membership verification. This issue can be exploited through a race condition when accessing the /common_teams API endpoint, allowing deactivated users to inadvertently gain knowledge of team names that they should not have access to. This poses a significant risk to user privacy and security within the platform.

Human OS v1.0:
Ageing Is an Unpatched Zero-Day Vulnerability.

Remediate biological technical debt. Prime Ageing uses 95% high-purity SIRT6 activation to maintain genomic integrity and bolster systemic resilience.

Deploy the Patch

Affected Version(s)

Mattermost 10.11.0 <= 10.11.9

Mattermost 11.3.0

Mattermost 10.11.10

References

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

CVSS V3.1

Score:
3.1
Severity:
LOW
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Juho Forsén
JSON
.