CVE-2026-6339

MEDIUM

Missing request origin validation on burn-on-read reveal endpoint

Title source: cna
STIX 2.1

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

References (1)

Core 1
Core References
Vendor Advisory vendor-advisory
MMSA-2026-00636
https://mattermost.com/security-updates

Scores

CVSS v3 4.3
EPSS 0.0002
EPSS Percentile 4.0%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-346
Status published
Products (6)
Mattermost/Mattermost 11.4.0 - 11.4.3
Mattermost/Mattermost 11.4.4
Mattermost/Mattermost 11.5.0 - 11.5.1
Mattermost/Mattermost 11.5.2
Mattermost/Mattermost 11.6.0
mattermost/mattermost_server 11.4.0 - 11.4.4
Published May 18, 2026
Tracked Since May 18, 2026