CVE-2026-67430CWE-401CWE-770

MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood

Medium · published July 29, 2026

CVSS v3.1
5.3
EPSS
1%
Percentile
42.3
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 expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.

The record
Technical detail
CVSS v3.1
5.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CVSS v4.0
Not supplied
EPSS
0.00507 · 42.3th percentile
Weaknesses
CWE-401 · Missing Release of Memory after Effective Lifetime; CWE-770 · Allocation of Resources Without Limits or Throttling
Published
2026-07-29T19:10Z
EPSS history
Timeline
  • 29 JUL 19:10Z
    MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood
    cvelistv5