CVE-2026-6339 Details
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
A vulnerability exists in Mattermost versions 11.5.x through 11.5.1 and 11.4.x through 11.4.3, where the application fails to properly validate the X-Requested-With header on the burn-on-read reveal endpoint. This flaw allows an authenticated channel member to reveal a burn-on-read message without the recipient's consent by using a manipulated Markdown image tag.
Users can upgrade to Mattermost versions 11.7.0 or 11.7.1 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 18, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://mattermost.com/security-updates | [email protected] | Vendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-346 | Origin Validation Error | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| mattermost mattermost server | >= 11.4.0, < 11.4.4 >= 11.5.0, < 11.5.2 |
CPE
Remediation
| |
Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 18, 2026 | Initial Analysis | [email protected] |
| May 18, 2026 | New CVE Received | [email protected] |