GHSA-C9XM-49CP-XCR9

rmcp OAuth client fetches server-controlled resource_metadata URLs

The direct impact is SSRF from any application embedding the rmcp OAuth client. Depending on where the client runs, this can reach:

• cloud metadata endpoints;
• localhost-only services;
• private VPC or container-network services;
• internal HTTP APIs not reachable from the attacker.

The attacker controls the URL through the MCP server response. The victim only needs to connect to the attacker's MCP server or a compromised server that can emit the crafted WWW-Authenticate header.

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

Kodem intelligence

Already deployed Kodem?

Before accepting or fetching a resource_metadata URL:

• require the URL to be same-origin with the original MCP server URL, unless the spec intentionally permits a narrow trusted exception;
• reject loopback, link-local, RFC 1918, unique-local IPv6, and known cloud metadata hostnames;
• reject non-HTTP(S) schemes;
• apply the same validation to redirect targets and any follow-on metadata URLs.

A minimal same-origin check would compare scheme, host, and effective port:

fn is_same_origin(base: &Url, candidate: &Url) -> bool {
    base.scheme() == candidate.scheme()
        && base.host() == candidate.host()
        && base.port_or_known_default() == candidate.port_or_known_default()
}

If cross-origin resource_metadata is required for compatibility, it should be explicitly opted into and protected by private-network blocking.

1. What is GHSA-C9XM-49CP-XCR9? GHSA-C9XM-49CP-XCR9 is a medium-severity server-side request forgery (SSRF) vulnerability in rmcp (rust), affecting versions < 2.0.0. It is fixed in 2.0.0. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. Which versions of rmcp are affected by GHSA-C9XM-49CP-XCR9? rmcp (rust) versions < 2.0.0 is affected.
3. Is there a fix for GHSA-C9XM-49CP-XCR9? Yes. GHSA-C9XM-49CP-XCR9 is fixed in 2.0.0. Upgrade to this version or later.
4. Is GHSA-C9XM-49CP-XCR9 exploitable, and should I be worried? Whether GHSA-C9XM-49CP-XCR9 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether GHSA-C9XM-49CP-XCR9 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix GHSA-C9XM-49CP-XCR9? Upgrade rmcp to 2.0.0 or later.

Other vulnerabilities in rmcp