CVE-2026-42559
RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.
Scoring
- Severity
- HIGH
- CVSS base score
- 8.8
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS probability
- 0.21%
- CWE
- CWE-346, CWE-350
- Published
- 2026-05-14
- Last modified
- 2026-05-14
Affected products
- modelcontextprotocol rust-sdk
Weakness type
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