What’s Vulnerable › Vulnerabilities

CVE-2026-33252: MCP Go SDK Allows Cross-Site Tool Execution for HTTP Servers without Authorizatrion

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-24 · updated 2026-06-17
• Weakness: CWE-352

Description

The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.1, 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. Version 1.4.1 contains a patch for the issue.

Affected products

• modelcontextprotocol go-sdk: before 1.4.1 — fixed in 1.4.1

How to fix

Upgrade to a fixed version: modelcontextprotocol go-sdk 1.4.1. Check the vendor advisory for mitigations.

References

• https://github.com/modelcontextprotocol/go-sdk/commit/a433a831d6e5d5ac3b9e625a8095aa8eaa040dfc
• https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-89xv-2j6f-qhc8

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