Endlessh: an SSH tarpit

Endlessh is an SSH tarpit that very slowly sends a randomized SSH banner. It keeps clients locked up for hours or even days at at time. The idea is that you put your real SSH server on another port and let the script kiddies themselves stuck in this tarpit instead of bothering real server.

Since the tarpit is in the banner before any cryptographic exchange occurs, this program doesn't depend on any cryptographic libraries. It's a simple, single-threaded, standalone C program. It uses poll() to trap multiple clients at a time.

Usage

Usage information is printed with -h.

Usage: endlessh [-vh] [-d MSECS] [-m LIMIT] [-p PORT]
  -d INT    Message millisecond delay [10000]
  -h        Print this help message and exit
  -m INT    Maximum number of clients [4096]
  -p INT    Listening port [2222]
  -v        Print diagnostics to standard output (repeatable)

The purpose of limiting the number of clients (-m) is to avoid tying up too many system resources with the tarpit. Clients beyond this limit are left in the accept queue, not rejected instantly.