# CVE-2026-63118

## Summary

- **CVE ID:** CVE-2026-63118
- **Severity:** MEDIUM
- **CVSS Score:** 6.9 (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)
- **CWE:** CWE-346, CWE-350
- **Published:** Jul 29, 2026
- **Last Modified:** Jul 29, 2026

## Description

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.

## Affected Products

- modelcontextprotocol — ruby-sdk (< 0.23.0)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.19%
- **EPSS Percentile:** 9.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._