The Go MCP SDK used Gos 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.
Weakness
The product initializes or sets a resource with a default that is intended to be changed by the product’s installer, administrator, or maintainer, but the default is not secure.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mcp_go_sdk | Lfprojects | * | 1.4.0 (excluding) |
| Red Hat OpenShift Dev Spaces 3.28 | RedHat | devspaces/udi-rhel9:1779829736 | * |
Related Attack Patterns
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