CVE-2026-90898CWE-284CWE-306broken-access-control

CVE-2026-90898

Critical · published September 14, 2026

CVSS v3.1
9.8
EPSS
2%
Percentile
83.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
9.8 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.02311 · 83.3th percentile
Weaknesses
CWE-284 · Improper Access Control; CWE-306 · Missing Authentication for Critical Function
Published
2026-09-14T15:17Z
References (4)
https://github.com/maximhq/bifrost · [email protected]https://github.com/maximhq/bifrost/commit/12e170352bd25eab1ae9ba16611f1797d1fd8fdc · [email protected]https://github.com/maximhq/bifrost/pull/6757 · [email protected]https://github.com/maximhq/bifrost/releases/tag/transports/v2.1.0 · [email protected]
EPSS history
Timeline
  • 17 SEP 03:33Z
    EPSS moved — → 0%
    epss
  • 14 SEP 10:18Z
    Bifrost unauthenticated remote code execution via MCP stdio client registration
    cvelistv5