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-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 vendored dependency at /vendor/cache/mcp-0.9.0.gem. Confirm how mcp is brought in through rubocop, then update it to the stated fixed version, 0.23.0. Done means the vulnerable mcp-0.9.0 dependency is no longer present in the lockfile or vendor cache.

Written by the indexing model from the issue text.