CVE-2026-34742
Published:April 02, 2026
Updated:August 06, 2026
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.
Affected Packages
https://github.com/modelcontextprotocol/go-sdk.git (GITHUB):
Affected version(s) >=v0.1.0 <v1.3.1Fix Suggestion:
Update to version v1.3.1github.com/modelcontextprotocol/go-sdk (GO):
Affected version(s) >=v0.0.0-20250509192946-b7672185059b <v1.4.0Fix Suggestion:
Update to version v1.4.0Related Resources (11)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.6
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
8.1
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
Weakness Type (CWE)
Initialization of a Resource with an Insecure Default
EPSS
Base Score:
0.46