Server panic via outgoing webhook responses
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641
Problem Types
| Type | CWE ID | Description |
|---|
| CWE | CWE-754 | CWE-754: Improper Check for Unusual or Exceptional Conditions |
Type: CWE
Description: CWE-754: Improper Check for Unusual or Exceptional Conditions
Metrics
| Version | Base score | Base severity | Vector |
|---|
| 3.1 | 6.5 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
Version: 3.1
Base score: 6.5
Base severity: MEDIUM
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H