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.

CVSS v3 5.9 MEDIUM

5.9^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.2 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97	Patch
https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2	Patch
https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685	Patch
https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb	Patch
https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874	Patch
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2	Product Release Notes
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35	Exploit Vendor Advisory
https://hackerone.com/reports/3556146	Permissions Required
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35	Exploit Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:lfprojects:mcp_ruby_sdk:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-03-27 22:16

Updated : 2026-06-17 10:38

NVD link : CVE-2026-33946

Mitre link : CVE-2026-33946

CVE.ORG link : CVE-2026-33946

JSON object : View

Products Affected

lfprojects

mcp_ruby_sdk

CWE

CWE-384

Session Fixation

CWE-639

Authorization Bypass Through User-Controlled Key

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