CVE-2026-34742 Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost
Attackers can bypass same-origin policy via DNS rebinding to interact with local MCP servers, potentially invoking tools or accessing resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-34742?
CVE-2026-34742 is a high-severity server-side request forgery vulnerability in modelcontextprotocol go-sdk, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
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.
Weakness: CWE-1188
Which versions are affected by CVE-2026-34742?
3 open source packages ship an affected version, including github.com/modelcontextprotocol/go-sdk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/modelcontextprotocol/go-sdk Go | All versions | 1.4.0 |
github.com/modelcontextprotocol/go-sdk Go | All versions | 1.4.0 |
github.com/modelcontextprotocol/go-sdk Go | All versions | 1.4.0 |
Products include Lfprojects Mcp Go Sdk.
How do I fix CVE-2026-34742?
Upgrade github.com/modelcontextprotocol/go-sdk to 1.4.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-34742 being exploited?
There is no known exploitation of CVE-2026-34742 in the wild and no public exploit code.
Other vulnerabilities in modelcontextprotocol go-sdk
Sources
Also known as CLEANSTART-2026-BU71031, CLEANSTART-2026-GU11984, GHSA-xw59-hvm2-8pj6, GO-2026-5771, MINI-35w4-5mqf-x5vp, MINI-p8vf-7524-pc7x.