CVE-2026-33946

MEDIUM

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

Title source: cna
STIX 2.1

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.

References (8)

Core 8
Core References
X_Refsource_Misc x_refsource_misc
https://hackerone.com/reports/3556146

Scores

CVSS v3 5.9
EPSS 0.0046
EPSS Percentile 36.5%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation poc
Automatable yes
Technical Impact partial

Details

CWE
CWE-384 CWE-639
Status published
Products (3)
lfprojects/mcp_ruby_sdk < 0.9.2
modelcontextprotocol/ruby-sdk < 0.9.2
rubygems/mcp 0 - 0.9.2RubyGems
Published Mar 27, 2026
Tracked Since Mar 29, 2026