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 a 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
trap multiple clients at a time.
Usage information is printed with
Usage: endlessh [-vh] [-d MS] [-f CONFIG] [-l LEN] [-m LIMIT] [-p PORT] -4 Bind to IPv4 only -6 Bind to IPv6 only -d INT Message millisecond delay  -f Set and load config file [/etc/endlessh/config] -h Print this help message and exit -l INT Maximum banner line length (3-255)  -m INT Maximum number of clients  -p INT Listening port  -v Print diagnostics to standard output (repeatable)
Argument order matters. The configuration file is loaded when the
argument is processed, so only the options that follow will override the
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 (
A SIGUSR1 signal will print connections stats to the log.
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 # Set the family of the listening socket # 0 = Use IPv4 Mapped IPv6 (Both v4 and v6, default) # 4 = Use IPv4 only # 6 = Use IPv6 only BindFamily 0
Some more esoteric systems require extra configuration when building.
RHEL 6 / CentOS 6
This system uses a version of glibc older than 2.17 (December 2012), and
clock_gettime(2) is still in librt. For these systems you will need to
link against librt:
Solaris / illumos
These systems don't include all the necessary functionality in libc and the linker requires some extra libraries:
make CC=gcc LDLIBS='-lnsl -lrt -lsocket'
If you're not using GCC or Clang, also override
to remove GCC-specific options. For example, on Solaris:
make CFLAGS=-fast LDFLAGS= LDLIBS='-lnsl -lrt -lsocket'
The feature test macros on these systems isn't reliable, so you may also
need to use