CVE-2026-6339

EUVD-2026-30749
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
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
MattermostCNA
4.3 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Base Score
CVSS 3.x
EPSS Score
Percentile: 2%
Affected Products (NVD)
VendorProductVersion
mattermostmattermost_server
11.4.0 ≤
𝑥
< 11.4.4
mattermostmattermost_server
11.5.0 ≤
𝑥
< 11.5.2
𝑥
= Vulnerable software versions
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
mattermostmattermost
11.5.0 ≤
𝑥
≤ 11.5.1
CNA
mattermostmattermost
11.4.0 ≤
𝑥
≤ 11.4.3
CNA
Common Weakness Enumeration
References
https://mattermost.com/security-updates