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CVE-2026-6339

MEDIUM CVSS: 4.3 Published: 2026-05-18 Modified: 2026-06-17

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 Platforms

Mattermost Mattermost Server

Weakness Type

CWE-346

References