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CVE-2026-33946

MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay

Published: Mar 27, 2026Updated: Apr 2, 2026 Sources: CVE List NVDCWE-384
NVD MITRE
5.9CVSSMEDIUM
EPSS Score
0.5%
Top 63.4%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:HPR:NUI:NS:UC:HI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-384CWE-639

Affected Products

mcp ruby sdklfprojects
Mixed
AI / ML / notebook-mlops
ruby-sdkmodelcontextprotocol
Mixed
AI / ML / ai-agent-tooling
lfprojectsoss-projectAI / MLaka mlflow, valkey, model context protocol servers, mcp servers
modelcontextprotocoloss-projectAI / MLaka mcp, model context protocol

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

2 techniques
Defense Evasion
Initial Access
View detailed technique mapping

References

https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97
github.com
https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
github.com
https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
github.com
and 5 more references View all →

Timeline

Published
Mar 27, 2026
Last Updated
Apr 2, 2026

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