Onyx, an open-source AI platform, has a vulnerability (CVE-2026-71424) involving exposure of sensitive OAuth Authorization headers through the GET /api/mcp/servers and GET /api/mcp/servers/persona/{persona_id} endpoints. The root cause is that OnyxTokenStorage.set_tokens and set_client_info copy per-user tokens into a shared admin MCPConnectionConfig row, which is then returned via auth_template.headers to any user with BASIC_ACCESS privileges. This allows unauthorized users to access another user's OAuth tokens. The vulnerability affects versions prior to 3.1.10, versions from 3.2.0 up to but not including 3.2.14, and versions from 3.3.0-beta.0 up to but not including 4.0.0. The issue is resolved in versions 3.1.10, 3.2.14, and 4.0.0.

The vulnerability allows unauthorized users with BASIC_ACCESS privileges to obtain other users' OAuth Authorization headers, potentially leading to unauthorized access to protected resources or impersonation of users. The CVSS score of 9.6 indicates a critical severity with high confidentiality and integrity impact but no availability impact.

Upgrade Onyx to version 3.1.10, 3.2.14, or 4.0.0 or later, where this vulnerability has been fixed. No additional mitigation is required once the system is updated to these versions.