Endlessh: an SSH tarpit

Endlessh is an SSH tarpit that very slowly sends an endless, random SSH banner. It keeps SSH clients locked up for hours or even days at at time. The purpose is to put your real SSH server on another port and then let the script kiddies get stuck in this tarpit instead of bothering a 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 MS] [-f CONFIG] [-l LEN] [-m LIMIT] [-p PORT]
  -d INT    Message millisecond delay [10000]
  -f        Set and load config file [/etc/endlessh/config]
  -h        Print this help message and exit
  -l INT    Maximum banner line length (3-255) [32]
  -m INT    Maximum number of clients [4096]
  -p INT    Listening port [2222]
  -v        Print diagnostics to standard output (repeatable)

Argument order matters. The configuration file is loaded when the -f argument is processed, so only the options that follow will override the configuration file.

By default no log messages are produced. The first -v enables basic logging and a second -v enables debugging logging (noisy). All log messages are sent to standard output.

endlessh -v >endlessh.log 2>endlessh.err

A SIGTERM signal will gracefully shut down the daemon, allowing it to write a complete, consistent log.

A SIGHUP signal requests a reload of the configuration file (-f).

Sample Configuration File

The configuration file has similar syntax to OpenSSH.

# The port on which to listen for new SSH connections.
Port 2222

# The endless banner is sent one line at a time. This is the delay
# in milliseconds between individual lines.
Delay 10000

# The length of each line is randomized. This controls the maximum
# length of each line. Shorter lines may keep clients on for longer if
# they give up after a certain number of bytes.
MaxLineLength 32

# Maximum number of connections to accept at a time. Connections beyond
# this are not immediately rejected, but will wait in the queue.
MaxClients 4096

# Set the detail level for the log.
#   0 = Quiet
#   1 = Standard, useful log messages
#   2 = Very noisy debugging information
LogLevel 0