high8.3
CVE-2026-67431
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients.
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rubygems | mcp | <= 0.22.0 | 0.23.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-5p9g-j988-pcwv
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv
- https://nvd.nist.gov/vuln/detail/CVE-2026-67431
- https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0