Vulnerability Details 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 valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 12.6%
CVSS Severity
CVSS v3 Score 5.9
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
Products affected by CVE-2026-33946
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.0.1
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.0.2
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.1.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.2.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.3.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.4.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.5.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.6.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.7.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.7.1
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.8.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.9.0
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cpe:2.3:a:lfprojects:mcp_ruby_sdk:0.9.1