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

Advisory record · `GHSA-g53w-w6mj-hrpp`

- **Identifiers:** `GHSA-g53w-w6mj-hrpp` · `GO-2026-5390`
- **State:** Confirmed
- **Severity:** CVSS 4.0, no score published
- **Critical:** No
- **Weakness (CWE):** [CWE-287](https://cwe.mitre.org/data/definitions/287.html) · [CWE-346](https://cwe.mitre.org/data/definitions/346.html) · [CWE-639](https://cwe.mitre.org/data/definitions/639.html)
- **Tags:** [Authentication bypass](https://agentprime.io/advisories/tag/auth-bypass.md) · [Broken access control](https://agentprime.io/advisories/tag/access-control.md) · [CWE-346](https://agentprime.io/advisories/tag/cwe-346.md)
- **Published:** 19 May 2026
- **Updated:** 21 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 19 May 2026, 19:42 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/Kuadrant/mcp-gateway` (Go): affected `<0.7.0`; fixed in `0.7.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> MCP Gateway (github.com/Kuadrant/mcp-gateway) versions before 0.7.0 are affected. A caller who can reach the router can send a request carrying a header that bypasses the gateway JWT session check and sets the upstream :authority header to a chosen value. The check depends on a shared router key that is a hardcoded fallback default and, in controller-managed deployments, a value derived from a non-secret resource UID, so the attacker can reach any backend registered with the gateway. Upgrade to version 0.7.0 or later.

Written 6 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- Score not published, CVSS 4.0: `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`, from GitHub Advisory Database

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 15:05 UTC: First seen by agentprime
- 31 Oct 2026, 15:05 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-g53w-w6mj-hrpp)

## Sources

- [GitHub Advisory Database: GHSA-g53w-w6mj-hrpp](https://github.com/advisories/GHSA-g53w-w6mj-hrpp)
- [OSV: GHSA-g53w-w6mj-hrpp](https://osv.dev/vulnerability/GHSA-g53w-w6mj-hrpp)
- <https://github.com/Kuadrant/mcp-gateway/security/advisories/GHSA-g53w-w6mj-hrpp>
- <https://github.com/Kuadrant/mcp-gateway/commit/6052079283472aff99727058c92618178f86b2d7>
- <https://github.com/Kuadrant/mcp-gateway>
- <https://github.com/Kuadrant/mcp-gateway/releases/tag/v0.7.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-g53w-w6mj-hrpp>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-g53w-w6mj-hrpp/>. Everything for agents: <https://agentprime.io/llms.txt>.