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Vulnerability · Published Apr 2, 2026 · Assigned by GitHub_M

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

High 8.0

In plain English

A high-severity security flaw in go-sdk from modelcontextprotocol. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.0High
Exploit odds (30 days)0.5%top 59.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/modelcontextprotocol/go-sdk1.4.0GHSA-xw59-hvm2-8pj6
Gogithub.com/modelcontextprotocol/go-sdk1.4.0GO-2026-5771

Affected products (as reported)

VendorProductVersions
modelcontextprotocol go-sdk < 1.4.0

Weakness: CWE-1188 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

References