CVE-2026-42559

Summary

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.

Affected Software

VendorProductVersion RangeStatus
modelcontextprotocolrust-sdk< 1.4.0affected

Weaknesses

  • CWE-346: CWE-346: Origin Validation Error
  • CWE-350: CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: total

References