CVE-2026-90898 Bifrost unauthenticated remote code execution via MCP stdio client registration
Unauthenticated attackers can register malicious MCP clients to execute arbitrary code on the Bifrost server due to disabled authentication by default.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-90898?
CVE-2026-90898 is a critical authentication bypass vulnerability in maximhq Bifrost, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-90898?
How do I fix CVE-2026-90898?
No fix has been published for CVE-2026-90898 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-90898 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-90898 exists.
Public exploit code: 1 Nuclei template and 1 proofs of concept on GitHub.
Sources
Also known as GHSA-gqjq-cgxr-8c7c.