Executive brief
Mattermost, a popular enterprise collaboration and messaging platform, is affected by a vulnerability that allows a logged-in user to crash specific plugin processes. By sending a specially crafted request to the Pull Request (PR) details interface, an attacker can cause a denial-of-service condition for that component. This disrupts normal operations and may require administrative intervention to restore full functionality.
Technical details
A denial-of-service vulnerability exists in Mattermost Server due to improper validation of specified input types (CWE-1287) within API request handlers. An authenticated attacker with network access to the Mattermost instance can send a specially crafted HTTP request to the Pull Request (PR) details endpoint. This malformed input causes the associated plugin process to crash. The vulnerability affects multiple version branches including 10.11.x, 11.4.x, 11.5.x, and 11.6.x. Patches have been released in versions 10.11.15, 11.4.5, 11.5.4, 11.6.1, and 11.7.0.
Affected products
- Mattermost Mattermost Server 11.6.0, 11.5.0 to 11.5.3, 11.4.0 to 11.4.4, 10.11.0 to 10.11.14
Timeline
- 2026-05-22: advisory: Mattermost published advisory MMSA-2026-00638
- 2026-05-22: disclosed: CVE-2026-4646 published to NVD