Add advisory for rmcp DNS rebinding

[DaleSeo]

Affected crate(s)

• rmcp (13,797,440 total downloads; 7,472,054 recent downloads per crates.io)

Links to upstream issue(s) or PR(s)

• GitHub Security Advisory: GHSA-89vp-x53w-74fx
• Fix PR: fix(http): add host check modelcontextprotocol/rust-sdk#764
• Upstream issue requesting a RustSec counterpart: RustSec advisory for GHSA-89vp-x53w-74fx? modelcontextprotocol/rust-sdk#846

Severity

High. A malicious public website could use DNS rebinding to send requests to a locally running rmcp Streamable HTTP server, allowing it to enumerate and invoke exposed MCP tools and access resources or prompts available through that server. The upstream GHSA uses CVSS 3.1 score 8.8.

Checklist

• Advisory filename(s) starts with RUSTSEC-0000-0000 as the ID
• date field is set to the public disclosure date
• Contains a concise and descriptive title after advisory metadata
• Asked maintainer(s) if publishing an advisory is appropriate

Testing

• Added the advisory under crates/rmcp/RUSTSEC-0000-0000.md using the RustSec template.
• Ran rustsec-admin lint; it currently stops on an existing pnet advisory before reaching this new file (crates.io package name does not match package name in advisory for pnet in RUSTSEC-2019-0037).