High severity · published May 14, 2026
CVE-2026-42559
RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport
8.8
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 19% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
RU
rust-sdk · modelcontextprotocol
< 1.4.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42559
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-42559
github.com
https://github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3
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/security/advisories/GHSA-89vp-x53w-74fx
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