GHSA-g53w-w6mj-hrpp
MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin "router-key" / "mcp-init-host" path
Blast Radius
github.com/Kuadrant/mcp-gatewayReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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 intocmd/mcp-broker-router/main.goas a fall-back default, and - in controller-managed deployments, a SHA-256 truncation of the
MCPGatewayExtensionUID — a non-secret value visible to anyone withgetpermission on the resource, and additionally exposed inargvbecause 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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/Kuadrant/mcp-gateway | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/Kuadrant/mcp-gateway. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of github.com/Kuadrant/mcp-gateway has shipped for GHSA-g53w-w6mj-hrpp yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-g53w-w6mj-hrpp is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-g53w-w6mj-hrpp. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-g53w-w6mj-hrpp in your dependencies?
O3 detects GHSA-g53w-w6mj-hrpp across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.