CVE-2026-63118 Details
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.
A vulnerability exists in the MCP Ruby SDK's Streamable HTTP transport, prior to version 0.23.0, allowing DNS rebinding attacks. The transport does not validate the HTTP Host or Origin headers, enabling a malicious web page to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.
Users can update to MCP Ruby SDK version 0.23.0 or later, where this vulnerability is fixed. For deployments behind a reverse proxy or bound to a non-loopback interface, it is recommended to configure the allowed_hosts and allowed_origins parameters to include the necessary values.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jul 29, 2026CISA-ADP
Assessed Jul 29, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a | [email protected] | Source CodeVendor |
| https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 | [email protected] | Release NotesVendor |
| https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-346 | Origin Validation Error | [email protected] |
| CWE-350 | Reliance on Reverse DNS Resolution for a Security-Critical Action | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Model Context Protocol MCP Ruby SDK | <= 0.22.0 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 29, 2026 | New CVE Received | [email protected] |
| Jul 29, 2026 | CVE Modified | CISA-ADP |