GHSA-89xv-2j6f-qhc8
Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk
Packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| Go | github.com/modelcontextprotocol/go-sdk | < 1.4.1 | 1.4.1 |
Details
As written in the advisory (Markdown source, shown as plain text).
The Go SDK's Streamable HTTP transport accepted browser-generated cross-site `POST` requests without validating the `Origin` header and without requiring `Content-Type: application/json`. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.
#### Impact:
A malicious website may have been able to send cross-site POST requests with `Content-Type: text/plain`, which due to CORS-safelisted properties would reach the MCP message handling without any CORS preflight barrier.
#### Fix:
The SDK was modified to perform `Content-Type` header validation for POST requests and introduced a configurable protection for verifying the origin of the request in commit a433a83. Users are advised to update to v1.4.1 to use this additional protection.
Note: v1.4.1 requires Go 1.25 or later.
#### Credits:
Thank you to Lê Minh Quân for reporting the issue.
References
External links from the advisory. They lead to third-party sites.