Update:

[CRITICAL] GHSA-g53w-w6mj-hrpp: MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin "router-key" / "mcp-init-host" path

GitHub Security Advisory·Security·SecurityFix·5/19/2026

## 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

Why it matters → github.com/kuadrant/mcp-gateway released an update. Review the changelog for relevant changes.

Who should care → Teams using github.com/kuadrant/mcp-gateway.

github.com/kuadrant/mcp-gateway

View original source ↗

Source payload preview

{
  "ghsaId": "GHSA-g53w-w6mj-hrpp",
  "summary": "MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin \"router-key\" / \"mcp-init-host\" path",
  "severity": "CRITICAL",
  "updatedAt": "2026-05-19T19:42:49Z",
  "references": [
    {
      "url": "https://github.com/Kuadrant/mcp-gateway/security/advisories/GHSA-g53w-w6mj-hrpp"
    },
    {
      "url": "https://github.com/advisories/GHSA-g53w-w6mj-hrpp"
    }
  ],
  "description": "## Summary\n \nThe MCP router (ext_proc) exposes an `initialize`-method code path that, when a\nrequest carries an `mcp-init-host` header, bypasses the gateway JWT session\nvalidator and rewrites the upstream `:authority` header to whatever the caller\nchooses, gated only by a single shared header value (`router-key`).
…