CVE-2026-90898

Bifrost unauthenticated remote code execution via MCP stdio client registration

Published: Sep 14, 2026Updated: Sep 18, 2026 Sources: CVE List NVDCWE-284

9.8CRITICAL

Description

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:NUser Interaction

None

Scope

S:UScope

Unchanged

Impact

C:HConfidentiality

High

I:HIntegrity

High

A:HAvailability

High

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Weaknesses

CWE-284 CWE-306

Affected Products

maximhq

Bifrost

Exploitability

0 exploit sources identified

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Official Patch Available

Workaround Available

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques

Initial Access

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References

https://github.com/maximhq/bifrost/pull/6757

github.com

https://github.com/maximhq/bifrost/commit/12e170352bd25eab1ae9ba16611f1797d1fd8fdc

github.com

https://github.com/maximhq/bifrost/releases/tag/transports/v2.1.0

github.com

and 1 more references View all →

News mentions

Critical Bifrost AI Gateway Flaw Lets Attackers Run Commands Without Credentials
en·The Hacker News·Sep 22, 2026 PoC Bifrost AI Gateway ai-ml

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