CVE-2026-63118: CWE-346: Origin Validation Error in modelcontextprotocol ruby-sdk
CVE-2026-63118 is a vulnerability in the MCP Ruby SDK prior to version 0.23.0 where the StreamableHTTPTransport component does not validate HTTP Host or Origin headers. This allows a malicious browser to perform DNS rebinding attacks to access a locally running MCP server and invoke exposed tools. The issue is fixed in version 0.23.0.
AI Analysis
Technical Summary
The MCP Ruby SDK's StreamableHTTPTransport component in versions before 0.23.0 fails to validate the HTTP Host and Origin request headers. This origin validation error (CWE-346) enables DNS rebinding attacks, allowing a malicious web page to bypass same-origin policies and interact with local MCP servers, potentially invoking exposed tools. The vulnerability is addressed in version 0.23.0.
Potential Impact
An attacker can exploit this vulnerability via a malicious browser page using DNS rebinding to reach a locally running MCP server and invoke exposed tools without proper origin validation. This could lead to unauthorized actions performed on the local MCP server. There are no known exploits in the wild as of the published date.
Mitigation Recommendations
Upgrade the MCP Ruby SDK to version 0.23.0 or later, where the origin validation issue is fixed. No other mitigation guidance is provided or necessary since the fix is available.
CVE-2026-63118: CWE-346: Origin Validation Error in modelcontextprotocol ruby-sdk
Description
CVE-2026-63118 is a vulnerability in the MCP Ruby SDK prior to version 0.23.0 where the StreamableHTTPTransport component does not validate HTTP Host or Origin headers. This allows a malicious browser to perform DNS rebinding attacks to access a locally running MCP server and invoke exposed tools. The issue is fixed in version 0.23.0.
CVSS v4.0
Score 6.9medium
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The MCP Ruby SDK's StreamableHTTPTransport component in versions before 0.23.0 fails to validate the HTTP Host and Origin request headers. This origin validation error (CWE-346) enables DNS rebinding attacks, allowing a malicious web page to bypass same-origin policies and interact with local MCP servers, potentially invoking exposed tools. The vulnerability is addressed in version 0.23.0.
Potential Impact
An attacker can exploit this vulnerability via a malicious browser page using DNS rebinding to reach a locally running MCP server and invoke exposed tools without proper origin validation. This could lead to unauthorized actions performed on the local MCP server. There are no known exploits in the wild as of the published date.
Mitigation Recommendations
Upgrade the MCP Ruby SDK to version 0.23.0 or later, where the origin validation issue is fixed. No other mitigation guidance is provided or necessary since the fix is available.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-15T16:54:55.816Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a6a53159c2644c7f8f0f0fd
Added to database: 07/29/2026, 19:23:01 UTC
Last enriched: 07/29/2026, 19:37:43 UTC
Last updated: 07/29/2026, 19:37:43 UTC
Views: 4
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