Vulnerability in Modelcontextprotocol Ruby-Sdk

CVE-2026-63118

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.

Published · last modified .

EPSS exploit prediction

EPSS: 0.002 (15.0th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 15.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-63118: held from 0.003 to 0.002.

EPSS over last 30 days · oldest: 0.003 · newest: 0.002 · change: -0.000

Affected products

Weakness classification (CWE)

References