RMCP: DNS rebinding vulnerability in rmcp Streamable HTTP server transport
Summary
| CVE | CVE-2026-42559 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-14 15:16:46 UTC |
| Updated | 2026-05-14 17:19:49 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 8.8 HIGH from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS: 0.000060000 probability, percentile 0.004250000 (date 2026-05-25)
Problem Types: CWE-346 | CWE-350 | CWE-346 CWE-346: Origin Validation Error | CWE-350 CWE-350: Reliance on Reverse DNS Resolution for a Security-Critical Action
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 8.8 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| 3.1 | CNA | DECLARED | 8.8 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
RequiredScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Modelcontextprotocol | Rust-sdk | affected < 1.4.0 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/modelcontextprotocol/rust-sdk/pull/764 | [email protected] | github.com | |
| github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x... | [email protected] | github.com | |
| github.com/modelcontextprotocol/rust-sdk/issues/822 | [email protected] | github.com | |
| github.com/modelcontextprotocol/rust-sdk/issues/815 | [email protected] | github.com | |
| github.com/modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c... | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.