CVE-2026-67431 (High) detected in mcp-0.9.0.gem

Vulnerable Library - mcp-0.9.0.gem

The official Ruby SDK for Model Context Protocol servers and clients

Library home page: https://rubygems.org/gems/mcp-0.9.0.gem

Path to dependency file: /Gemfile.lock

Path to vulnerable library: /vendor/cache/mcp-0.9.0.gem

Dependency Hierarchy:

• manageiq-style-1.6.0.gem (Root Library)
  • rubocop-performance-1.26.1.gem
    • rubocop-1.85.1.gem
      • ❌ mcp-0.9.0.gem (Vulnerable Library)

Found in base branch: master

Vulnerability Details

MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.

Publish Date: 2026-07-29

URL: CVE-2026-67431

CVSS 3 Score Details (8.2)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: High
  • Availability Impact: Low

Suggested Fix

Type: Upgrade version

Origin: https://github.com/advisories/GHSA-5p9g-j988-pcwv

Release Date: 2026-07-29

Fix Resolution: mcp - 0.23.0