CVE-2026-34742

The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.0, the Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with StreamableHTTPHandler or SSEHandler, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances. This issue has been patched in version 1.4.0.

CVSS v3 8.1 HIGH

8.1^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.8 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d	Patch
https://github.com/modelcontextprotocol/go-sdk/pull/760	Issue Tracking Patch
https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0	Release Notes
https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6	Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:21772
https://access.redhat.com/security/cve/CVE-2026-34742
https://bugzilla.redhat.com/show_bug.cgi?id=2454608
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34742.json

Configurations

Configuration 1 (hide)

cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-04-02 19:21

Updated : 2026-07-24 21:10

NVD link : CVE-2026-34742

Mitre link : CVE-2026-34742

CVE.ORG link : CVE-2026-34742

JSON object : View

Products Affected

lfprojects

mcp_go_sdk

CWE

CWE-1188

Initialization of a Resource with an Insecure Default

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Prior to version 1.4.0, the Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with StreamableHTTPHandler or SSEHandler, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances. This issue has been patched in version 1.4.0."}, {"lang": "es", "value": "El SDK Go de MCP utilizaba el encoding/json est\u00e1ndar de Go. Antes de la versi\u00f3n 1.4.0, el SDK Go del Protocolo de Contexto del Modelo (MCP) no habilita la protecci\u00f3n contra el rebinding de DNS por defecto para servidores basados en HTTP. Cuando un servidor MCP basado en HTTP se ejecuta en localhost sin autenticaci\u00f3n con StreamableHTTPHandler o SSEHandler, un sitio web malicioso podr\u00eda explotar el rebinding de DNS para eludir las restricciones de la pol\u00edtica de mismo origen y enviar solicitudes al servidor MCP local. Esto podr\u00eda permitir a un atacante invocar herramientas o acceder a recursos expuestos por el servidor MCP en nombre del usuario en esas circunstancias limitadas. Este problema ha sido parcheado en la versi\u00f3n 1.4.0."}], "lastModified": "2026-07-24T21:10:00.143", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "92CB3EED-2D8E-4ADC-BD05-2A14C13CA7DA", "versionEndExcluding": "1.4.0"}], "operator": "OR"}]}], "sourceIdentifier": "security-advisories@github.com"}