CVE-2026-6347: Mattermost Calls plugin exposes TURN server credentials in plaintext in support packets

Severity: high (CVSS 7.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-18 · updated 2026-10-14
Weakness: CWE-200

Description

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugin configuration.. Mattermost Advisory ID: MMSA-2026-00605

Affected products

Mattermost: from 10.11.0 before 10.11.14; from 11.4.0 before 11.4.4; from 11.5.0 before 11.5.2 — fixed in 10.11.14, 11.4.4, 11.5.2

How to fix

Upgrade to a fixed version: Mattermost 10.11.14, 11.4.4, 11.5.2. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

Get alerted when CVE-2026-6347 or the next vulnerability affects your stack