Raw vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:NSummary
CVE-2025-9076 is a medium-severity Missing Authorization (CWE-862) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 6.5 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation of Remote Services (T1210); ranked at the 16th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-29165
Vulnerability Data
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…
more
channels enabled.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Missing authorization (CWE-862) in shared channel sync directly enables a compromised/malicious remote cluster to obtain sensitive data, mapping to exploitation of the remote federation service.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly enforces authorization checks on user data objects before they are exposed during shared-channel synchronization to remote clusters.
Enforces information-flow policies that restrict which user attributes may leave the local system to external/shared-channel peers.
Limits the privileges granted to remote-cluster accounts so they cannot receive unsanitized sensitive user data even if synchronization occurs.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Explicitly requires defining, enforcing, and reviewing authorizations and least privilege, directly preventing missing authorization checks.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Requiring authentication and credentials before any access occurs eliminates the absence of authorization checks that would otherwise allow an unauthenticated actor to reach protected resources.
Requiring formal authorization of every access request before rights are granted ensures that checks for required permissions are performed, preventing missing authorization checks from being introduced.
Mandatory authorization checks and central records of granted rights ensure that every access attempt is preceded by an explicit decision rather than relying on missing checks.
Segregating the approval of access rights from their implementation provides an independent check that reduces the impact of missing authorization checks in the resulting system configuration.
By requiring competent outsiders to verify that every function enforces the need-to-know principle, the control lowers the likelihood that missing authorization checks persist undetected.
Defining authorization responsibilities and reviewing risk-treatment progress throughout the project lifecycle catches missing authorization checks before the system is deployed.