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.
Published: 2026-04-02
Score: 7.6 High
EPSS: < 1% Very Low
KEV: No
Impact: Remote Code Execution
Action: Immediate Patch
AI Analysis

Impact

The Model Context Protocol Go SDK omits DNS rebinding protection for HTTP‑based servers before version 1.4.0. When an MCP server runs on localhost without authentication, a malicious site can perform DNS rebinding to circumvent same‑origin policy and issue arbitrary requests to the local server. This exposure may let an attacker invoke backend tools or retrieve data exposed by the MCP server, effectively enabling remote code execution or unauthorized data access. The weakness is identified as CWE‑1188.

Affected Systems

Affected are developers using the Model Context Protocol Go SDK. Any deployment of the SDK older than version 1.4.0 that exposes an HTTP server over localhost and does not employ authentication is vulnerable. The patch that disables the default vulnerability was introduced in release v1.4.0.

Risk and Exploitability

The CVSS score of 7.6 signals a high severity, and while the EPSS is not available, the lack of KEV listing suggests that market damage is not yet observed. Attackers can exploit this flaw by hosting a malicious webpage that triggers DNS rebinding, especially if the victim’s browser has an active session with the local MCP server. Because the server is assumed to be on localhost and unauthenticated, the attack typically requires the victim’s browser to be tricked into making the rebinding request.

Generated by OpenCVE AI on April 2, 2026 at 22:23 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade to Model Context Protocol Go SDK version 1.4.0 or later.
  • If an upgrade is not possible, put the MCP server behind a firewall and restrict it to non‑localhost interfaces or require authentication.
  • Enable DNS rebinding protection manually, if the SDK supports it, to re‑enable the default safeguard.
  • Ensure that unauthenticated access to the MCP server is removed or tightly sandboxed.

Generated by OpenCVE AI on April 2, 2026 at 22:23 UTC.

Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-xw59-hvm2-8pj6 DNS Rebinding Protection Disabled by Default in Model Context Protocol Go SDK for Servers Running on Localhost
History

Fri, 03 Apr 2026 20:15:00 +0000

Type Values Removed Values Added
First Time appeared Lfprojects
Lfprojects mcp Go Sdk
CPEs cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*
Vendors & Products Lfprojects
Lfprojects mcp Go Sdk
Metrics cvssV3_1

{'score': 8.0, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N'}

 cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N'}

Fri, 03 Apr 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Fri, 03 Apr 2026 10:15:00 +0000

Type Values Removed Values Added
First Time appeared Modelcontextprotocol
Modelcontextprotocol go-sdk
Vendors & Products Modelcontextprotocol
Modelcontextprotocol go-sdk

Fri, 03 Apr 2026 01:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 8.0, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N'}

threat_severity

Important

Thu, 02 Apr 2026 20:30:00 +0000

Type Values Removed Values Added
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.
Title Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost
Weaknesses CWE-1188
References
Metrics cvssV4_0

{'score': 7.6, 'vector': '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'}

Subscriptions

Lfprojects Mcp Go Sdk
Modelcontextprotocol Go-sdk
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-04-03T15:59:37.091Z

Reserved: 2026-03-30T19:17:10.224Z

Link: CVE-2026-34742

cve-icon Vulnrichment

Updated: 2026-04-03T15:59:03.748Z

cve-icon NVD

Status : Analyzed

Published: 2026-04-02T19:21:33.023

Modified: 2026-04-03T19:48:25.627

Link: CVE-2026-34742

cve-icon Redhat

Severity : Important

Publid Date: 2026-04-02T18:32:34Z

Links: CVE-2026-34742 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-04-03T09:16:40Z

Weaknesses