CVE-2026-42559
RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport
CVSS Score
8.8
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-346 CWE-350 |
| Vendor | modelcontextprotocol |
| Product | rust-sdk |
| Published | May 14, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Affected Versions
modelcontextprotocol / rust-sdk
< 1.4.0
References
github.com: https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx github.com: https://github.com/modelcontextprotocol/rust-sdk/issues/815 github.com: https://github.com/modelcontextprotocol/rust-sdk/issues/822 github.com: https://github.com/modelcontextprotocol/rust-sdk/pull/764 github.com: https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3