CVE intelligence and bounded remediation
CVE-2026-6341 — Mattermost Mattermost Server security vulnerability
Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked group via direct API requests. Mattermost Advisory ID: MMSA-2026-00602
- Severity
- Medium
- CVSS
- 4.3 (3.1)
- Published
- 2026-05-18
- CISA KEV
- Not currently listed
- Ecosystem
- software/application
- Weaknesses
- CWE-863
Affected products
- mattermost / mattermost_server
Showing 1 representative product identities from 3 source matches. Confirm exact affected versions with the linked vendor and NVD evidence.
Matched remediation archetype
Authorization bypass, IDOR, and cross-tenant access
This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.
Check exposure
- Map object and action authorization checks across API, UI, batch, import/export, and background-job paths.
- Identify tenant, ownership, role, and policy boundaries for affected resources and administrative operations.
- Use synthetic fixtures to compare intended access matrices without accessing another user's real data.
Remediate safely
- Enforce server-side authorization at each resource access and state transition using the authenticated principal and trusted tenant context.
- Scope data queries by tenant and ownership; treat client-supplied identifiers, roles, and policy claims as untrusted.
- Add deny-by-default policy tests for horizontal and vertical access across every affected transport.
Authoritative sources
Complete CVE record and remediation plan
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