MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDKs streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victims Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.
Weakness
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mcp_ruby_sdk | Lfprojects | * | 0.9.2 (excluding) |
Extended Description
Such a scenario is commonly observed when:
In the generic exploit of session fixation vulnerabilities, an attacker creates a new session on a web application and records the associated session identifier. The attacker then causes the victim to associate, and possibly authenticate, against the server using that session identifier, giving the attacker access to the user’s account through the active session.
Potential Mitigations
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/196.html
- https://cwe.mitre.org/data/definitions/21.html
- https://cwe.mitre.org/data/definitions/31.html
- https://cwe.mitre.org/data/definitions/39.html
- https://cwe.mitre.org/data/definitions/59.html
- https://cwe.mitre.org/data/definitions/60.html
- https://cwe.mitre.org/data/definitions/61.html
References
- https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97
- https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
- https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
- https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
- https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
- https://hackerone.com/reports/3556146
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35