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
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.003 (15.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 15.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Mattermost — versions 10.10.0, 10.11.0, 10.10.2
- Mattermost Server
Weakness classification (CWE)
Public proof-of-concept exploits
References
- mattermost.com/security-updates (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.