CVE-2026-63119 (Medium) detected in mcp-0.9.0.gem

[mend-bolt-for-github]

CVE-2026-63119 - Medium Severity Vulnerability

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:

• rubocop-1.85.1.gem (Root Library)
  • ❌ 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::StdioTransport and MCP::Client::Stdio in the mcp gem use IO#gets without a byte limit, allowing a peer that sends data without a newline to exhaust process memory. This issue is fixed in version 0.23.0.

Publish Date: 2026-07-29

URL: CVE-2026-63119

CVSS 3 Score Details (6.2)

Base Score Metrics:

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

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: GHSA-7683-3w9x-ch42

Release Date: 2026-07-29

Fix Resolution: mcp - 0.23.0

---

Step up your Open Source Security Game with Mend here