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CVE-2026-90898

Bifrost unauthenticated remote code execution via MCP stdio client registration

CVSS 3.1 9.8 CRITICALCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-90898

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-90898

Published

github.com/maximhq/bifrost/transports

https://github.com/maximhq/bifrost

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "maximhq",
                    "product": "Bifrost",
                    "platforms": [
                        "Linux",
                        "macOS"
                    ],
                    "collectionURL": "https://github.com/maximhq/bifrost",
                    "packageName": "github.com/maximhq/bifrost/transports",
                    "repo": "git://github.com/maximhq/bifrost",
                    "modules": [
                        "transports/bifrost-http",
                        "core/mcp"
                    ],
                    "programFiles": [
                        "transports/bifrost-http/handlers/mcp.go",
                        "transports/bifrost-http/handlers/middlewares.go"
                    ],
                    "versions": [
                        {
                            "status": "affected",
                            "version": "0",
                            "lessThan": "2.1.0",
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }

Original source record · Cite this exact observation · Complete original publisher JSON