CVE-2025-66414: DNS Rebinding Protection Disabled by Default in Model Context Protocol TypeScript SDK for Servers Running on Localhost
MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. Prior to 1.24.0, The Model Context Protocol (MCP) TypeScript 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 StreamableHTTPServerTransport or SSEServerTransport and has not enabled enableDnsRebindingProtection, 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. Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport. This vulnerability is fixed in 1.24.0.
Other sources
The Model Context Protocol (MCP) TypeScript 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 StreamableHTTPServerTransport or SSEServerTransport and has not enabled enableDnsRebindingProtection, 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.
Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport.
Servers created via createMcpExpressApp() now have this protection enabled by default when binding to localhost. Users with custom Express configurations are advised to update to version 1.24.0 and apply the exported hostHeaderValidation() middleware when running an unauthenticated server on localhost.
— GitHub
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2025-66414?
CVE-2025-66414 is considered to have a medium severity due to potential DNS rebinding attacks on HTTP servers.
How do I fix CVE-2025-66414?
To fix CVE-2025-66414, upgrade the MCP TypeScript SDK to version 1.24.0 or later.
What vulnerability does CVE-2025-66414 address?
CVE-2025-66414 addresses the lack of DNS rebinding protection in the MCP TypeScript SDK for HTTP-based servers.
Is CVE-2025-66414 present in all versions of the MCP TypeScript SDK?
CVE-2025-66414 affects all versions of the MCP TypeScript SDK prior to 1.24.0.
What are the implications of CVE-2025-66414 for developers?
Developers using the affected versions of the MCP TypeScript SDK should implement updates to avoid potential security vulnerabilities.