DNS Rebinding Affecting mcp package, versions <0.23.0
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-RUBY-MCP-18016342
- published19 Jul 2026
- disclosed17 Jul 2026
- credittonghuaroot, KairoKid, HE WEI
Introduced: 17 Jul 2026
CVE-2026-63118 (opens in a new tab)How to fix?
Upgrade mcp to version 0.23.0 or higher.
Overview
mcp is a The official Ruby SDK for Model Context Protocol servers and clients
Affected versions of this package are vulnerable to DNS Rebinding in the handle_post method of MCP::Server::Transports::StreamableHTTPTransport in lib/mcp/server/transports/streamable_http_transport.rb, which processes JSON-RPC requests after checking Accept, Content-Type, Mcp-Session-Id, and protocol version but never reads HTTP_HOST or HTTP_ORIGIN. An attacker can drive a victim's locally running MCP server, invoke its exposed tools, and exfiltrate their output such as files, secrets, or command results by luring the victim to a webpage that rebinds its hostname to a loopback address and posts JSON-RPC requests with forged Host and Origin headers. Exploitation requires the victim to run the server on a reachable HTTP port over loopback or the LAN and to visit the attacker's page, and the impact depends on which tools the server exposes.