CVE-2026-33252
HIGH7.1EPSS 0.01%Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk
Description
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.
Affected packages (2)
- Go/github.com/modelcontextprotocol/go-sdkfrom 0, < 1.4.1
- Go/github.com/modelcontextprotocol/go-sdkfrom 0, < 1.4.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L |