CVE-2026-33946

HIGH EPSS 36.9%
Published Mar 27, 20263mo ago · Modified Jun 17, 20261w ago
8.2 CVSS 4.0
High
Find Similar
Published Mar 27, 2026 3mo ago
Last Modified Jun 17, 2026 1w ago

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 Details

Base Score
8.2
Exploitability
—
Impact
—
Vector string
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
36.9% percentile
Exploit & Patch Status
Public Exploit Known
Patch Available

Weaknesses 2

CWE-384
CWE-639

Affected Products 1

VendorProductVersionRange
lfprojectsmcp_ruby_sdk* <0.9.2

References 8

  • github.com https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97
    Patch
  • github.com https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
    Patch
  • github.com https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
    Patch
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
    Patch
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
    Patch
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
    ProductRelease Notes
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
    ExploitVendor Advisory
  • hackerone.com https://hackerone.com/reports/3556146
    Permissions Required

Remediation

  • github.com https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97
    Patch
  • github.com https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
    Patch
  • github.com https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
    Patch
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
    Patch
  • github.com https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
    Patch