CVE-2026-67431CWE-284

MCP Ruby SDK: Ruby SSE Session Poisoning

High · published July 29, 2026

CVSS v4.0
8.3
EPSS
0%
Percentile
40.4
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
8.3 · HIGH
Vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
EPSS
0.00480 · 40.4th percentile
Weakness
CWE-284 · Improper Access Control
Published
2026-07-29T19:15Z
EPSS history
Timeline
  • 29 JUL 19:15Z
    MCP Ruby SDK: Ruby SSE Session Poisoning
    cvelistv5