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GHSA-g53w-w6mj-hrpp
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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