# CVE-2026-90898: Bifrost - Authentication Bypass

> Live exploitation tracking for CVE-2026-90898 by the CrowdSec Live Exploit Tracker, built from real-world attack data crowdsourced from CrowdSec's global network.

Page: https://tracker.crowdsec.net/cves/CVE-2026-90898

## Key facts

- **Exploitation phase:** Limited Exploitation. The vulnerability is known but shows very limited attacker interest or exploitation activity.
- **CVSS score:** 9.8
- **Public exploit available:** Yes
- **Affected products:** Maximhq Bifrost
- **Weaknesses:** CWE-306 (Missing Authentication for Critical Function); CWE-284 (Improper Access Control)
- **Tags:** ai_mcp

## 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.

## CrowdSec analysis

[CVE-2026-90898](https://euvd.enisa.europa.eu/vulnerability/CVE-2026-90898) is a critical authentication bypass vulnerability in Bifrost that can let unauthenticated attackers register a stdio MCP client through the management API and execute programs as the Bifrost process user. The flaw affects transports/v2.0.0 and could enable remote code execution, potentially compromising the confidentiality, integrity, and availability of the gateway.

CrowdSec has been tracking this vulnerability and its exploits since 20th of October 2026.

CrowdSec has not observed any significant exploitation activity targeting CVE-2026-90898 across its network. As a result, no community-driven trend analysis is available for this vulnerability at this time.

Attackers target the `/api/mcp/client` endpoint with an unauthenticated MCP client registration using `connection_type: "stdio"` and a crafted command in `stdio_config`. Outbound callbacks may indicate that the configured command executed on the Bifrost gateway.

## Timeline

- 2026-09-14: CVE Published. CVE-2026-90898 is published to NVD.
- 2026-10-20: Rule Released. CrowdSec releases a rule to detect CVE-2026-90898 exploitation attempts against the CrowdSec Network.

## References

- https://github.com/maximhq/bifrost/commit/12e170352bd25eab1ae9ba16611f1797d1fd8fdc
- https://github.com/maximhq/bifrost
- https://github.com/maximhq/bifrost/pull/6757
- https://github.com/maximhq/bifrost/releases/tag/transports/v2.1.0
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-90898.yaml

## Live exploitation data

The [Live Exploit Tracker page](https://tracker.crowdsec.net/cves/CVE-2026-90898) follows observed exploitation activity for CVE-2026-90898. [Request an API key](https://tracker.crowdsec.net/request-api-key) for full access to its exploitation timeline, attacking IP addresses and blocklists.