GHSA-xvcx-mgpc-5xh3MediumCVSS 4.3

Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint

Published
May 18, 2026
Last Modified
June 1, 2026

🔗 CVE IDs covered (1)

CVE-2026-6339 →

📋 Description

Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636

🎯 Affected products4

  • go/github.com/mattermost/mattermost/server/v8:>= 11.5.0, < 11.5.2
  • go/github.com/mattermost/mattermost/server/v8:>= 11.4.0, < 11.4.4
  • go/github.com/mattermost/mattermost/server/v8:< 8.0.0-20260327001745-7a339a6438f5
  • go/github.com/mattermost/mattermost-server:< 5.3.2-0.20260327001745-7a339a6438f5

🔗 References (4)