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CVE-2026-90898

CriticalPublished

Bifrost unauthenticated remote code execution via MCP stdio client registration

Published: Sep 14, 2026
Updated: Sep 14, 2026
Assigning CNA: JFROG
Evidence observed: Sep 23, 2026

Primary CVSS

9.8/ 10Critical

nvd · CVSS 3.1

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

EPSS probability estimate

0.3%

Low · next 30 days

Percentile: 27.9%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

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.

Sources

CVE-2026-90898PoC
Educational CVE-2026-90898 proof-of-concept repository for authorized security research, vulnerability awareness, and defensive testing in isolated lab environments.

Responsible use

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