What is CVE-2025-9076?

CVE-2025-9076 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 6.5/10. Published 2025-09-15.

How severe is CVE-2025-9076?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Is CVE-2025-9076 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Auth bypass in Mattermost

CVE-2025-9076

Mattermost versions 10.10.x <= 10.10.1 fail to properly sanitize user data during shared channel membership synchronization, which allows malicious or compromised remote clusters to access sensitive user information via unsanitized user objects. This vulnerability affects Mattermost Server instances with shared channels enabled.

Vulnerability class: Broken Access Control

EPSS: 0.002 (15.5th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N.

Affected products

Mattermost — versions 10.10.0, 10.11.0, 10.10.2
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-862 — Missing Authorization

Public proof-of-concept exploits

fkie-cad/nvd-json-data-feeds

References

responsibledisclosure@mattermost.com (Vendor Advisory)

Frequently asked questions

What is CVE-2025-9076?: CVE-2025-9076 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 6.5/10. Published 2025-09-15.
How severe is CVE-2025-9076?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2025-9076 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.