PT-2026-41657 · Mattermost · Mattermost

Game0V3R · Published 2026-05-18 · Updated 2026-05-18 · CVE-2026-6339

Positive Technologies (AI Summary)

CVSS v3.1

4.3

Medium

Base vector

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

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.4.x through 11.4.3 Mattermost versions 11.5.x through 11.5.1

Description An issue exists where the burn-on-read reveal endpoint fails to validate the 'X-Requested-With' header. This allows an authenticated channel member to force the reveal of a burn-on-read message without the recipient's consent by using a crafted Markdown image tag.

Recommendations Update Mattermost versions 11.4.x through 11.4.3 to a version later than 11.4.3. Update Mattermost versions 11.5.x through 11.5.1 to a version later than 11.5.1.

Fix

Origin Validation Error

Weakness Enumeration

CWE-346

Related Identifiers

CVE-2026-6339

Affected Products

Mattermost

References · 5

• https://mattermost.com/security-updates · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-6339 · Security Note
• https://t.me/CVEtracker/54117 · Telegram Post
• https://twitter.com/VulmonFeeds/status/2056335671451582795 · Twitter Post
• https://twitter.com/CVEarity/status/2056409697222349026 · Twitter Post