Answer in brief
CVE-2026-90898 records a Critical severity (CVSS 9.8) vulnerability in Bifrost unauthenticated remote code execution via MCP stdio client registration. The current sources do not mark it as known exploited. The current feed maps maximhq/Bifrost (generic), maximhq/github.com/maximhq/bifrost/transports (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps maximhq/Bifrost (generic), maximhq/github.com/maximhq/bifrost/transports (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| maximhq/Bifrostgeneric | >=0 <2.1.0 | 2.1.0 |
| maximhq/github.com/maximhq/bifrost/transportsgeneric | >=0 <2.1.0 | 2.1.0 |
Published upstream
Sep 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 18, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 14, 2026
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.
Quoted source text, attributed separately from HOL analysis.