PT-2026-65898 · Modelcontextprotocol · Ruby-Sdk

CVE-2026-67431 · Published 2026-07-29 · Updated 2026-07-29

Mitre

CVSS v4.0

8.3

High

Base vector

AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

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.

Fix

Improper Access Control

Weakness Enumeration

CWE-284

Related Identifiers

CVE-2026-67431

Affected Products

Ruby-Sdk

References · 4

• https://nvd.nist.gov/vuln/detail/CVE-2026-67431 · Security Note
• https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv · Note
• https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 · Note
• https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356 · Note