CVE-2026-6339: Missing request origin validation on burn-on-read reveal endpoint
Medium · CVSS 4.3 (CVSS 3.1)EPSS 0.11%, 1th percentilePublished Updated Assigner: Mattermost
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
Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L · CWE-346
Tracked companies
Mapped from the CVE’s affected-product data, NVD CPE matches, vendor advisories or package feeds. A mapping means the vendor’s software is named, not that its hosted service was exposed.
Status incidents that name it
No tracked status incident names this CVE.
Affected vendors and products
Mattermost: Mattermost
References
- CVE record on cve.org (opens in new tab)
- NVD entry (opens in new tab)
- mattermost.com/security-updates (opens in new tab)
- CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (opens in new tab)
- This product uses data from the NVD API but is not endorsed or certified by the NVD. (opens in new tab)
- Known Exploited Vulnerabilities catalog from CISA. (opens in new tab)
- EPSS scores from FIRST (Exploit Prediction Scoring System). (opens in new tab)