CVE-2026-67431 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 bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.
A vulnerability exists in the MCP Ruby SDK, specifically in versions through 0.22.0, within the Streamable HTTP transport implementation. The issue arises because the transport does not associate session IDs with their respective owners. This flaw allows an attacker with a stolen session ID to execute tools in the context of the victim's session, leading to unauthorized actions. The vulnerability is particularly insidious as it can be exploited without the victim's knowledge, causing their session to be silently compromised.
Users can update to MCP Ruby SDK version 0.23.0 or later, where this vulnerability has been addressed by adding session ownership validation in the Streamable HTTP transport.
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 30, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356 | [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-5p9g-j988-pcwv | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-284 | Improper Access Control | [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 30, 2026 | CVE Modified | CISA-ADP |
| Jul 29, 2026 | New CVE Received | [email protected] |