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

Nobody has claimed this yet.

## CVE-2026-67431 - 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 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

For more information on CVSS3 Scores, click here.

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

***
Step up your Open Source Security Game with Mend [here](https://www.whitesourcesoftware.com/full_solution_bolt_github)

Start with /Gemfile.lock and /vendor/cache/mcp-0.9.0.gem to trace how mcp 0.9.0 is resolved through the RuboCop dependencies. Update the dependency resolution to mcp 0.23.0 or later, then verify that the vulnerable cached gem and lockfile entry are replaced and the repository's dependency checks pass.

Written by the indexing model from the issue text.