Auth bypass in Modelcontextprotocol Ruby-sdk
CVE-2026-33946
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a…
EPSS: 0.001 (20.2th percentile) — read the EPSS interpretation.
Affected products
- Modelcontextprotocol Ruby-sdk — versions < 0.9.2
Weakness classification (CWE)
References
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35 (x_refsource_CONFIRM)
- https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874 (x_refsource_MISC)
- https://hackerone.com/reports/3556146 (x_refsource_MISC)
- https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97 (x_refsource_MISC)
- https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2 (x_refsource_MISC)
- https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685 (x_refsource_MISC)
- https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb (x_refsource_MISC)
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2 (x_refsource_MISC)