CVE-2026-34742: Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost

Description

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 vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

Required

Confidentiality

High

Integrity

High

Availability

None

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.5% · higher than 39% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

GO

go-sdk · modelcontextprotocol

< 1.4.0 · source: vendor

MG

Mcp GO Sdk · Lfprojects

before 1.4.0 · source: NVD

MT

Migration Toolkit for Virtualization · Red Hat

All versions, or not specified · source: CISA

OS

OpenShift Serverless · Red Hat

All versions, or not specified · source: CISA

RH

Red Hat OpenShift Dev Spaces 3.28 · Red Hat

All versions, or not specified · source: CISA