CVE intelligence and bounded remediation
CVE-2026-3473 — Mattermost Mattermost Server security vulnerability
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620
- Severity
- High
- CVSS
- 7.1 (3.1)
- Published
- 2026-05-22
- CISA KEV
- Not currently listed
- Ecosystem
- software/application
- Weaknesses
- CWE-639
Affected products
- mattermost / mattermost_server
Showing 1 representative product identities from 4 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
The detailed catalog view below loads this exact record, its source evidence, and the full seven-phase agentic change plan.