PT-2026-65888 · Modelcontextprotocol · Ruby-Sdk

CVE-2026-63118 · Published 2026-07-29 · Updated 2026-07-29

Mitre

CVSS v4.0

6.9

Medium

Base vector

AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

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.

Exploit

Fix

Origin Validation Error

Weakness Enumeration

CWE-346

CWE-350

Related Identifiers

CVE-2026-63118

Affected Products

Ruby-Sdk

References · 4

• 🔥 https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m · Exploit
• https://nvd.nist.gov/vuln/detail/CVE-2026-63118 · Security Note
• https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 · Note
• https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a · Note