CVE-2025-4128: Mattermost Guest User Information Disclosure Vulnerability

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: 2025-06-11 · updated 2026-06-17
Weakness: CWE-863

Description

Mattermost versions 10.5.x <= 10.5.4, 9.11.x <= 9.11.13 fail to properly restrict API access to team information, allowing guest users to bypass permissions and view information about public teams they are not members of via a direct API call to /api/v4/teams/{team_id}.

Affected products

Mattermost: from 9.11.0 before 9.11.14; from 10.5.0 before 10.5.5 — fixed in 10.5.5, 9.11.14

How to fix

Upgrade to a fixed version: Mattermost 10.5.5, 9.11.14. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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