CVE-2026-33946

low-risk
Published 2026-03-27

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.

Do I need to act?

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0.04% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
5
CVSS 5.9/10 Medium
NETWORK / HIGH complexity

Affected Products (1)

Mcp Ruby Sdk

Affected Vendors

Lfprojects

References (9)

Patch https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextPro...
Patch https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C...
Patch https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/stre...
Patch https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_h...
Patch https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec...
Product https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
Exploit https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5...
Permissions Required https://hackerone.com/reports/3556146
Exploit https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5...
23
/ 100
low-risk
Severity 18/34 · Moderate
Exploitability 0/34 · Minimal
Exposure 5/34 · Minimal