CVE-2026-6339

🔶 medium

Summary

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

CVSS Score

4.3

Medium

EPSS Score

0.0

Exploit Probability

Published Date

2026-05-18

First Seen: 2026-05-19

📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 5.3% of all 348,695 vulnerabilities in our database.

#330,067

Below average severity

Severity Percentile

🎯 CISA SSVC Assessment Updated: May 18, 2026

🔍 Exploitation Status

None

No known exploits

⚙️ Automatable

Requires human interaction

💥 Technical Impact

Partial

Limited system impact

🏆 Discovered By

game0v3r

SSVC data provided by CISA

Last Modified 2026-05-18

Source NVD 🔗

CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CWE IDs (Weakness Types)

CWE-346

📦 Affected Products 2

Vendor	Product	Status	Affected Versions
mattermost	mattermost_server	Affected	> 11.4.0 < 11.4.4
mattermost	mattermost_server	Affected	> 11.5.0 < 11.5.2

🔗 References 1

https://mattermost.com/security-updates

Vendor Advisory

🔗 Related CVEs 6

CVE ID	Severity	CVSS	EPSS	Summary	Published
CVE-2026-10527	🔶 medium	6.3	0.2	Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to reconcile SchemeAdmin flags with a ...	2026-08-17
CVE-2026-15754	🔶 medium	4.2	0.2	Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate ...	2026-08-17
CVE-2026-16044	🔶 medium	5.4	0.2	Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to prevent guest users from receiving Board Admin privile...	2026-08-17
CVE-2026-16045	🔶 medium	4.3	0.2	Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 Mattermost failed to restrict OAuth deauthorization and person...	2026-08-17
CVE-2026-16046	🔶 medium	4.3	0.2	Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to enforce run-state validation on write operations for f...	2026-08-17
CVE-2026-16047	🔶 medium	4.3	0.2	Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access...	2026-08-17

These CVEs affect the same products