CVE-2026-90898: Maximhq Bifrost

Critical severity, CVSS 9.8. EPSS: 0.6% chance of exploitation in the next 30 days.

Bifrost registers MCP clients through its management API. A stdio client is a command plus args. Bifrost starts that program in the gateway the moment the client is added. No MCP handshake required. The default is governance.auth_config.is_enabled=false. Auth off means every caller is a local admin. One unauthenticated POST /api/mcp/client is enough to run a program as the Bifrost process user (appuser on the official image).  transports/v2.1.0 refuses an unauthenticated stdio registration with 403. transports/v2.0.0 still allows it.

Affected products

• Maximhq Bifrost: before 2.1.0 (fixed in 2.1.0)

Published 2026-09-14. Last modified 2026-09-18.