CVE-2026-67431

Received Received - Intake

Session Hijacking in MCP Ruby SDK

Publication date: 2026-07-29

Last updated on: 2026-07-29

Assigner: GitHub, Inc.

Description

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.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-07-29

Last Modified

2026-07-29

Generated

2026-07-30

AI Q&A

2026-07-30

EPSS Evaluated

N/A

NVD

CVE-2026-67431

Affected Vendors & Products

Vendor	Product	Version / Range
mcp	ruby_sdk	to 0.23.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-284	The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

Attack-Flow Graph

Executive Summary

The MCP Ruby SDK before version 0.23.0 has a vulnerability where the session ID is not bound to a specific session owner. This allows an attacker with a stolen session ID to send tool call requests that execute within the victim's session.

Impact Analysis

An attacker could misuse a stolen session ID to execute unauthorized tool calls in your session, potentially leading to data breaches, unauthorized actions, or further compromise of your system.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations may face compliance violations, legal penalties, and reputational damage if exploited.

Mitigation Strategies

Upgrade the MCP Ruby SDK to version 0.23.0 or later to address the session ID binding issue.

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