CVE-2026-63118
MediumCVSS 6.9Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
A vulnerability in MCP Ruby SDK before version 0.23.0 allows DNS rebinding attacks due to missing validation of Host and Origin headers in StreamableHTTPTransport. A malicious web page can access a local MCP server and invoke tools.
Risk Assessment
An attacker could remotely invoke tools on a local MCP server, potentially leading to unauthorized actions in the system.
Recommendation
Upgrade MCP Ruby SDK to version 0.23.0 or later.
Other vulnerabilities in MCP Ruby SDK
See all- CVE-2026-67432High
MCP Ruby SDK before version 0.23.0 in StreamableHTTPTransport reads the entire JSON-RPC POST body without size limits, allowing an unauthenticated remote attacker to exhaust process memory.
- CVE-2026-67431High
MCP Ruby SDK before version 0.23.0 does not bind a session ID to its owner, allowing an attacker with a stolen session ID to send tools/call requests in the victim's session.
- CVE-2026-67430Medium
A vulnerability in MCP Ruby SDK before version 0.23.0 allows process memory exhaustion via unbounded creation of ServerSession objects in StreamableHTTPTransport. Sessions do not expire by default, and repeated initialize requests accumulate objects.
- CVE-2026-63119Medium
A vulnerability in MCP Ruby SDK before version 0.23.0 allows process memory exhaustion by sending data without a newline in StdioTransport and Stdio client. The IO#gets function is used without a byte limit.
Original NVD description (English source)
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.