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© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2026-42559

31
FAUCET Score

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.

First published: May 14, 2026Last modified: May 14, 2026

Impacted Technologies

VendorProductVersion(s)CPE
ModelcontextprotocolRust-Sdk
< 1.4.0CNA affected

CVSS Data

CVSS version used by this source: 3.1

8.8HIGH

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 Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.21%
Probability of exploitation in next 30 days
EPSS Percentile
11.7%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0021 is in the 11th percentile among its peer group of 14,855 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

rustpatch availablevia ghsa
Product: rmcpFixed in: 1.4.0

Vendor Advisories (1)

rustGHSA-89vp-x53w-74fxhigh

rmcp Streamable HTTP server transport has a DNS rebinding vulnerability

May 6, 2026

References

github.com / modelcontextprotocol/rust-sdk/commit/8e22aa2de28df5a285eed87c11cd89bf15fa90d3
github.com / modelcontextprotocol/rust-sdk/issues/815
github.com / modelcontextprotocol/rust-sdk/issues/822
github.com / modelcontextprotocol/rust-sdk/pull/764
github.com / modelcontextprotocol/rust-sdk/security/advisories/GHSA-89vp-x53w-74fx