What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-02 · updated 2026-07-24
• Weakness: CWE-1188

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 products

• modelcontextprotocol go-sdk: before 1.4.0 — fixed in 1.4.0

How to fix

Upgrade to a fixed version: modelcontextprotocol go-sdk 1.4.0. Check the vendor advisory for mitigations.

References

• https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d
• https://github.com/modelcontextprotocol/go-sdk/pull/760
• https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0
• https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6
• https://access.redhat.com/errata/RHSA-2026:21772
• https://access.redhat.com/security/cve/CVE-2026-34742
• https://bugzilla.redhat.com/show_bug.cgi?id=2454608
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34742.json

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