CVE-2026-63118

UNKNOWN 0.0

MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection

CVSS Score

0.0

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-346 CWE-350
Vendor	modelcontextprotocol
Product	ruby-sdk
Published	Jul 29, 2026
Last Updated	Jul 29, 2026

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Affected Versions

modelcontextprotocol / ruby-sdk

< 0.23.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m github.com: https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a github.com: https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0