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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
5.9MEDIUM
NVD MITRE
EPSS Score
0.5%
Top 62.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
Not 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.

No summary for this CVE yet.

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

lfprojects
oss-projectaka mlflow, model context protocol servers, mcp servers, valkey
mcp ruby sdkLibraryLibrary
AI / ML / ml-framework
modelcontextprotocol
oss-projectaka mcp, model context protocol
ruby-sdkMixed
AI / ML / ai-agent-tooling

Exploitability

Official Patch Available

Attack Graph

Products CVE Techniques Tactics

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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 →

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