CVE-2026-6339
MEDIUM
NVD
CVSS Score
4.3
Severity
MEDIUM
Published
May 18, 2026
Vendor
unknown
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