CVE-2026-67431

UNKNOWN 0.0

MCP Ruby SDK: Ruby SSE Session Poisoning

CVSS Score

0.0

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-284
Vendor	modelcontextprotocol
Product	ruby-sdk
Published	Jul 29, 2026

Stay Ahead of the Next One

Get instant alerts for modelcontextprotocol ruby-sdk

Be the first to know when new unknown vulnerabilities affecting modelcontextprotocol ruby-sdk are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

Affected Versions

modelcontextprotocol / ruby-sdk

< 0.23.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv github.com: https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356 github.com: https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0