# GHSA-g53w-w6mj-hrpp: The MCP router (ext_proc) exposes an `initialize`-method code path that, when a request carries an `mcp-init-host` header, bypass

> Unauthenticated attackers can bypass JWT validation and inject authority headers to access backend services via the MCP router's initialize path.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 May 2026
- **Also known as:** GO-2026-5390

## What is GHSA-g53w-w6mj-hrpp?

GHSA-g53w-w6mj-hrpp is an authentication bypass vulnerability in github.com/Kuadrant/mcp-gateway, published on 19 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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 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.

## Which versions are affected by GHSA-g53w-w6mj-hrpp?

3 open source packages ship an affected version, including github.com/Kuadrant/mcp-gateway.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/Kuadrant/mcp-gateway` | Go | All versions | None |
| `github.com/Kuadrant/mcp-gateway` | Go | All versions | 0.7.0 |
| `github.com/Kuadrant/mcp-gateway` | Go | All versions | 0.7.0 |

## How do I fix GHSA-g53w-w6mj-hrpp?

Upgrade github.com/Kuadrant/mcp-gateway to 0.7.0 or later.

## Is GHSA-g53w-w6mj-hrpp being exploited?

There is no known exploitation of GHSA-g53w-w6mj-hrpp in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-g53w-w6mj-hrpp and fix it if it is affected.

What it is: GHSA-g53w-w6mj-hrpp is an authentication bypass vulnerability in github.com/Kuadrant/mcp-gateway, published on 19 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-g53w-w6mj-hrpp in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/Kuadrant/mcp-gateway (Go): affected all versions; no fix listed
- github.com/Kuadrant/mcp-gateway (Go): affected all versions; fixed in 0.7.0
- github.com/Kuadrant/mcp-gateway (Go): affected all versions; fixed in 0.7.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-g53w-w6mj-hrpp/ (Markdown: https://insights.sbomify.com/GHSA-g53w-w6mj-hrpp/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-g53w-w6mj-hrpp

---
From sbomify Insights: https://insights.sbomify.com/GHSA-g53w-w6mj-hrpp/
Summaries are generated and may contain mistakes; the official description above is the record.