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Vulnerability record · CVE-2026-90898 · published 14 September 2026

CVE-2026-90898: Improper access control vulnerability

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.

9.8 CVSS 3.1 Critical EPSS 0.62% · top 52.3% CWE-284 · Improper access controlCWE-306 · Missing authentication for critical function Awaiting Analysis
9.8CVSS 3.1 base score
0.62%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
18 Sep 2026Last modified by NVD

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.

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

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-90898), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.