CVE-2026-63118 (High) detected in mcp-0.9.0.gem

## CVE-2026-63118 - High 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:
- manageiq-style-1.6.0.gem (Root Library)
- rubocop-performance-1.26.1.gem
- rubocop-1.85.1.gem
- :x: **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 validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.

Publish Date: 2026-07-29

URL: CVE-2026-63118

CVSS 3 Score Details (7.4)

Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: Low
- Privileges Required: None
- User Interaction: Required
- Scope: Changed
- Impact Metrics:
- Confidentiality Impact: High
- Integrity Impact: None
- Availability Impact: None

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: https://github.com/advisories/GHSA-rjr6-rcgv-9m7m

Release Date: 2026-07-29

Fix Resolution: mcp - 0.23.0

***
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Start with Gemfile.lock and the cached dependency at vendor/cache/mcp-0.9.0.gem; trace how mcp is brought in through rubocop-performance and rubocop. Update the dependency path so mcp resolves to 0.23.0, then confirm the lockfile and cached library no longer contain the vulnerable 0.9.0 version.

Written by the indexing model from the issue text.