CVE-2026-67431
High
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.
SeverityHigh
CVSS8.3
Exploit probability—
ProductModelcontextprotocol Ruby-sdk
PublishedJul 29, 2026
First seenJul 29, 2026
Weakness typeCWE-284Improper access control
How to fix
Sources list no fixed version or patch link for this vulnerability.
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| modelcontextprotocol ruby-sdk | < 0.23.0 | — |
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