CVE-2026-63118
Medium · CVSS 6.9Published 2026-07-29
CVSS
6.9
Medium
EPSS
—
exploit probability
Active Exploit
No
not yet listed
What is 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.
CVSS Score Explained
CVSS 6.9 is Medium severity. Exploitation usually requires some specific conditions (local access, user interaction, or a particular config). Still worth patching in your next maintenance window.
EPSS Exploitation Probability
No EPSS score yet — model needs more data on this CVE.
References & Patches
- ›https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a
- PATCHhttps://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
- ›https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m
- ›https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m
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