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

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Summary

CVECVE-2026-34742
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-02 19:21:33 UTC
Updated2026-04-02 19:21:33 UTC
DescriptionThe 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.

Risk And Classification

Primary CVSS: v4.0 7.6 HIGH from [email protected]

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-1188 | CWE-1188 CWE-1188: Insecure Default Initialization of Resource

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary7.6HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED7.6HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
Passive
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Go-sdk affected < 1.4.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/go-sdk/pull/760 [email protected] github.com
github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm... [email protected] github.com
github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976... [email protected] github.com
github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0 [email protected] github.com
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