modelcontextprotocol rust-sdk up to 1.3.x streamable_http_server origin validation

CVSS Meta Temp Score
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CTI Interest Score
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7.4$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as critical, was found in modelcontextprotocol rust-sdk up to 1.3.x. This affects an unknown part of the file crates/rmcp/src/transport/streamable_http_server/. Executing a manipulation can lead to origin validation. The identification of this vulnerability is CVE-2026-42559. The attack may be launched remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in modelcontextprotocol rust-sdk up to 1.3.x. It has been declared as critical. This vulnerability affects some unknown functionality of the file crates/rmcp/src/transport/streamable_http_server/. The manipulation with an unknown input leads to a origin validation vulnerability. The CWE definition for the vulnerability is CWE-346. The product does not properly verify that the source of data or communication is valid. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-42559 since 04/28/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available.

Upgrading to version 1.4.0 eliminates this vulnerability. Applying the patch 8e22aa2de28df5a285eed87c11cd89bf15fa90d3 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.6
VulDB Meta Temp Score: 7.4

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 8.8
CNA Vector (GitHub_M): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Origin validation
CWE: CWE-346 / CWE-345
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: rust-sdk 1.4.0
Patch: 8e22aa2de28df5a285eed87c11cd89bf15fa90d3

Timelineinfo

04/28/2026 CVE reserved
05/14/2026 +16 days Advisory disclosed
05/14/2026 +0 days VulDB entry created
05/14/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: 815
Status: Confirmed

CVE: CVE-2026-42559 (🔒)
GCVE (CVE): GCVE-0-2026-42559
GCVE (VulDB): GCVE-100-363904

Entryinfo

Created: 05/14/2026 17:33
Changes: 05/14/2026 17:33 (66)
Complete: 🔍
Cache ID: 216::103

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