MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
Present
Additional conditions required
Privileges Required
None
No privileges needed
User Interaction
Active
User action required
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
None
No data modification
Availability
None
No disruption
CVSS Vector v4.0
Weakness Type (CWE)
References 3
https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b2946…
security-advisories@github.com
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
security-advisories@github.com
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-…
security-advisories@github.com