# CVE-2026-33946

## Summary

- **CVE ID:** CVE-2026-33946
- **Severity:** HIGH
- **CVSS Score:** 8.2 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-384, CWE-639
- **Published:** Mar 27, 2026
- **Last Modified:** Mar 30, 2026

## Description

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.

## Affected Products

- modelcontextprotocol — ruby-sdk (< 0.9.2)

## References

- [CNA](https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35)
- [CNA](https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874)
- [CNA](https://hackerone.com/reports/3556146)
- [CNA](https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97)
- [CNA](https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2)
- [CNA](https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685)
- [CNA](https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb)
- [CNA](https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.46%
- **EPSS Percentile:** 38.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._