CVE-2026-6339

Published May 18, 2026

Last updated 7 days ago

Overview

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
Source
responsibledisclosure@mattermost.com
NVD status
Analyzed
Products
mattermost_server

Risk scores

CVSS 3.1

Type
Primary
Base score
4.3
Impact score
1.4
Exploitability score
2.8
Vector string
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Severity
MEDIUM

Weaknesses

responsibledisclosure@mattermost.com
CWE-346

Social media

Hype score
Not currently trending

Configurations

References

Sources include official advisories and independent security research.