CVE-2026-63118CWE-346CWE-350

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

Medium · published July 29, 2026

CVSS v4.0
6.9
EPSS
0%
Percentile
16.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
6.9 · MEDIUM
Vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N
EPSS
0.00256 · 16.3th percentile
Weaknesses
CWE-346 · Origin Validation Error; CWE-350 · Reliance on Reverse DNS Resolution for a Security-Critical Action
Published
2026-07-29T19:07Z
EPSS history
Timeline
  • 29 JUL 19:07Z
    MCP Ruby SDK: Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection
    cvelistv5