CVE-2026-6339

MEDIUM CVSS 4.3 View on NVD ↗

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

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Affected Products

mattermost/mattermost_server

References

https://mattermost.com/security-updates

Published: May 18, 2026 09:16 UTC Modified: May 18, 2026 19:11 UTC