Vulnerability 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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Lfprojects | Mcp Go Sdk | < 1.4.0 |
Related Weaknesses (CWE)
References
- https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976Patch
- https://github.com/modelcontextprotocol/go-sdk/pull/760Issue TrackingPatch
- https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0Release Notes
- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvmVendor Advisory
FAQ
What is CVE-2026-34742?
CVE-2026-34742 is a vulnerability with a CVSS score of 8.1 (HIGH). 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 HTT...
How severe is CVE-2026-34742?
CVE-2026-34742 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-34742?
Check the references section above for vendor advisories and patch information. Affected products include: Lfprojects Mcp Go Sdk.