CVE-2026-90898

9.8 criticalEPSS 2.3%

Critical (9.8). EPSS 2.3% 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.

Severity

CVSS 3.1

9.8 critical

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 2.3% chance of exploitation in the next 30 days; higher than 83% of CVEs (scores of 2026-10-31)
CWEs: CWE-284, CWE-306
Published: 2026-09-14
Modified: 2026-09-18
Record from: the NVD, synced 2026-10-19

References

https://github.com/maximhq/bifrost
https://github.com/maximhq/bifrost/commit/12e170352bd25eab1ae9ba16611f1797d1fd8fdc
https://github.com/maximhq/bifrost/pull/6757
https://github.com/maximhq/bifrost/releases/tag/transports/v2.1.0

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