GHSA-5gmf-x7hg-97wfMediumCVSS 6.5

Mattermost doesn't filter nil elements from outgoing webhook attachment payloads before processing

Published
May 26, 2026
Last Modified
June 30, 2026

🔗 CVE IDs covered (1)

CVE-2026-4915 →

📋 Description

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

🎯 Affected products5

  • go/github.com/mattermost/mattermost-server:= 11.6.0
  • go/github.com/mattermost/mattermost-server:>= 11.5.0, < 11.5.4
  • go/github.com/mattermost/mattermost-server:>= 11.4.0, < 11.4.5
  • go/github.com/mattermost/mattermost-server:>= 10.11.0, < 10.11.15
  • go/github.com/mattermost/mattermost/server/v8:< 8.0.0-20260407102538-faa7d75b4ea0

🔗 References (4)