Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests.. Mattermost Advisory ID: MMSA-2026-00624
| Vendor | Product | Versions |
|---|---|---|
| mattermost | mattermost | 10.11.0, 11.5.0, 11.4.0, 11.3.0, 10.11.15, 11.4.5, 11.5.4, 11.6.1 |
Updated affected versions, changed severity to HIGH, and marked the vulnerability as actively exploited with an exploit available.
Updated severity to CRITICAL and noted that no exploit exists.
Initial creation
