Security Advisory

CVE-2026-6339

CVE vulnerability detail - eXtreme Datacenter Security Operations

Published 2026-05-18 08:05:30

Last updated 2026-05-18 12:42:01

Assigner Mattermost

CVSS score 4.3

State PUBLISHED

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

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