CVE-2025-11776: Guest user can discover archived public channels

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-11-14 · updated 2026-10-19
Weakness: CWE-863

Description

Mattermost versions <11 fail to properly restrict access to archived channel search API which allows guest users to discover archived public channels via the `/api/v4/teams/{team_id}/channels/search_archived` endpoint

Affected products

Mattermost: before 11.0.0 — fixed in 11.0.0

How to fix

Upgrade to a fixed version: Mattermost 11.0.0. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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