GHSA-g53w-w6mj-hrpp

Source

https://github.com/advisories/GHSA-g53w-w6mj-hrpp

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-g53w-w6mj-hrpp/GHSA-g53w-w6mj-hrpp.json

JSON Data

https://api.osv.dev/v1/vulns/GHSA-g53w-w6mj-hrpp

Aliases

GO-2026-5390

Published

2026-05-19T19:42:46Z

Modified

2026-07-21T15:00:41Z

Severity

9.3 (Critical) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N CVSS Calculator

Summary

MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin "router-key" / "mcp-init-host" path

Details

Summary

The MCP router (ext_proc) exposes an initialize-method code path that, when a request carries an mcp-init-host header, bypasses the gateway JWT session validator and rewrites the upstream :authority header to whatever the caller chooses, gated only by a single shared header value (router-key). The shared value is

a literal string (secret-api-key) baked into cmd/mcp-broker-router/main.go as a fall-back default, and
in controller-managed deployments, a SHA-256 truncation of the MCPGatewayExtension UID — a non-secret value visible to anyone with get permission on the resource, and additionally exposed in argv because it is passed to the broker-router container via --mcp-router-key=....

A request that satisfies the trivial header check is forwarded to any backend listener registered with the gateway (including external services such as api.githubcopilot.com when configured), bypassing both the broker (where the signed x-mcp-authorized capability filter is enforced) and the gateway's JWT-based session model.

Database specific

{
    "cwe_ids":  [
        "CWE-287",
        "CWE-346",
        "CWE-639"
    ],
    "github_reviewed":  true,
    "github_reviewed_at":  "2026-05-19T19:42:46Z",
    "nvd_published_at":  null,
    "severity":  "CRITICAL"
}

References

Affected packages

Go / github.com/Kuadrant/mcp-gateway

Package

Name: github.com/Kuadrant/mcp-gateway; View open source insights on deps.dev
Purl: pkg:golang/github.com/Kuadrant/mcp-gateway

Affected ranges

Type: SEMVER
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Fixed

0.7.0

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-g53w-w6mj-hrpp/GHSA-g53w-w6mj-hrpp.json"