CVE-2026-6339CWE-346

CVE-2026-6339

Medium · published May 18, 2026

CVSS v3.1
4.3
EPSS
0%
Percentile
4.4
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
4.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CVSS v4.0
Not supplied
EPSS
0.00157 · 4.4th percentile
Weakness
CWE-346 · Origin Validation Error
Published
2026-05-18T13:16Z
Affected products (2)
ProductVersionsFixed in
mattermost/mattermost_server≥ 11.4.0, < 11.4.411.4.4
mattermost/mattermost_server≥ 11.5.0, < 11.5.211.5.2
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 18 MAY 08:05Z
    Missing request origin validation on burn-on-read reveal endpoint
    cvelistv5