T1140

Description from ATT&CK

Adversaries may use Obfuscated Files or Information to hide artifacts of an intrusion from analysis. They may require separate mechanisms to decode or deobfuscate that information depending on how they intend to use it. Methods for doing that include built-in functionality of malware or by using utilities present on the system.

One such example is the use of certutil to decode a remote access tool portable executable file that has been hidden inside a certificate file.(Citation: Malwarebytes Targeted Attack against Saudi Arabia) Another example is using the Windows copy /b or type command to reassemble binary fragments into a malicious payload.(Citation: Carbon Black Obfuscation Sept 2016)(Citation: Sentinel One Tainted Love 2023)

Sometimes a user's action may be required to open it for deobfuscation or decryption as part of User Execution. The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary.(Citation: Volexity PowerDuke November 2016)

Atomic Tests

Atomic Test #1 - Deobfuscate/Decode Files Or Information
Atomic Test #2 - Certutil Rename and Decode
Atomic Test #3 - Base64 decoding with Python
Atomic Test #4 - Base64 decoding with Perl
Atomic Test #5 - Base64 decoding with shell utilities
Atomic Test #6 - Base64 decoding with shell utilities (freebsd)
Atomic Test #7 - FreeBSD b64encode Shebang in CLI
Atomic Test #8 - Hex decoding with shell utilities
Atomic Test #9 - Linux Base64 Encoded Shebang in CLI
Atomic Test #10 - XOR decoding and command execution using Python
Atomic Test #11 - Expand CAB with expand.exe

Atomic Test #1 - Deobfuscate/Decode Files Or Information

Encode/Decode executable Upon execution a file named T1140_calc_decoded.exe will be placed in the temp folder

Supported Platforms: Windows

auto_generated_guid: dc6fe391-69e6-4506-bd06-ea5eeb4082f8

Inputs:

Name	Description	Type	Default Value
executable	name of executable	path	C:\Windows\System32\calc.exe

Attack Commands: Run with `command_prompt`!

certutil -encode #{executable} %temp%\T1140_calc.txt
certutil -decode %temp%\T1140_calc.txt %temp%\T1140_calc_decoded.exe

Cleanup Commands:

del %temp%\T1140_calc.txt >nul 2>&1
del %temp%\T1140_calc_decoded.exe >nul 2>&1

Atomic Test #2 - Certutil Rename and Decode

Rename certutil and decode a file. This is in reference to latest research by FireEye here

Supported Platforms: Windows

auto_generated_guid: 71abc534-3c05-4d0c-80f7-cbe93cb2aa94

Inputs:

Name	Description	Type	Default Value
executable	name of executable/file to decode	path	C:\Windows\System32\calc.exe

Attack Commands: Run with `command_prompt`!

copy %windir%\system32\certutil.exe %temp%\tcm.tmp
%temp%\tcm.tmp -encode #{executable} %temp%\T1140_calc2.txt
%temp%\tcm.tmp -decode %temp%\T1140_calc2.txt %temp%\T1140_calc2_decoded.exe

Cleanup Commands:

del %temp%\tcm.tmp >nul 2>&1
del %temp%\T1140_calc2.txt >nul 2>&1
del %temp%\T1140_calc2_decoded.exe >nul 2>&1

Atomic Test #3 - Base64 decoding with Python

Use Python to decode a base64-encoded text string and echo it to the console

Supported Platforms: Linux, macOS

auto_generated_guid: 356dc0e8-684f-4428-bb94-9313998ad608

Inputs:

Name	Description	Type	Default Value
message	Message to print to the screen	string	Hello from Atomic Red Team test T1140!
encoded_file	File to temporarily save encoded text	path	/tmp/T1140.encoded

Attack Commands: Run with `sh`!

ENCODED=$(python3 -c 'import base64;enc=base64.b64encode("#{message}".encode());print(enc.decode())')
python3 -c "import base64;dec=base64.b64decode(\"$ENCODED\");print(dec.decode())"
python3 -c "import base64 as d;dec=d.b64decode(\"$ENCODED\");print(dec.decode())"
python3 -c "from base64 import b64decode;dec=b64decode(\"$ENCODED\");print(dec.decode())"
python3 -c "from base64 import b64decode as d;dec=d(\"$ENCODED\");print(dec.decode())"
echo $ENCODED | python3 -c "import base64,sys;dec=base64.b64decode(sys.stdin.read());print(dec.decode())"
echo $ENCODED > #{encoded_file} && python3 -c "import base64;dec=base64.b64decode(open('#{encoded_file}').read());print(dec.decode())"

Dependencies: Run with `sh`!

Description: Python must be present

Check Prereq Commands:

which python3

Get Prereq Commands:

echo "Please install Python 3"

Atomic Test #4 - Base64 decoding with Perl

Use Perl to decode a base64-encoded text string and echo it to the console

Supported Platforms: Linux, macOS

auto_generated_guid: 6604d964-b9f6-4d4b-8ce8-499829a14d0a

Inputs:

Name	Description	Type	Default Value
message	Message to print to the screen	string	Hello from Atomic Red Team test T1140!
encoded_file	File to temporarily save encoded text	path	/tmp/T1140.encoded

Attack Commands: Run with `sh`!

ENCODED=$(perl -e "use MIME::Base64;print(encode_base64('#{message}'));")
perl -le "use MIME::Base64;print(decode_base64('$ENCODED'));"
echo $ENCODED | perl -le 'use MIME::Base64;print(decode_base64(<STDIN>));'
echo $ENCODED > #{encoded_file} && perl -le 'use MIME::Base64;open($f,"<","#{encoded_file}");print(decode_base64(<$f>));'

Dependencies: Run with `sh`!

Description: Perl must be present

Check Prereq Commands:

which perl

Get Prereq Commands:

echo "Please install Perl"

Atomic Test #5 - Base64 decoding with shell utilities

Use common shell utilities to decode a base64-encoded text string and echo it to the console

Supported Platforms: Linux, macOS

auto_generated_guid: b4f6a567-a27a-41e5-b8ef-ac4b4008bb7e

Inputs:

Name	Description	Type	Default Value
message	Message to print to the screen	string	Hello from Atomic Red Team test T1140!
encoded_file	File to temporarily save encoded text	path	/tmp/T1140.encoded

Attack Commands: Run with `sh`!

ENCODED=$(echo '#{message}' | base64)
printf $ENCODED | base64 -d
echo $ENCODED | base64 -d
echo $(echo $ENCODED) | base64 -d
echo $ENCODED > #{encoded_file} && base64 -d #{encoded_file}
echo $ENCODED > #{encoded_file} && base64 -d < #{encoded_file}
echo $ENCODED > #{encoded_file} && cat #{encoded_file} | base64 -d
echo $ENCODED > #{encoded_file} && cat < #{encoded_file} | base64 -d
bash -c "{echo,\"$(echo $ENCODED)\"}|{base64,-d}"

Atomic Test #6 - Base64 decoding with shell utilities (freebsd)

Use common shell utilities to decode a base64-encoded text string and echo it to the console

Supported Platforms: Linux

auto_generated_guid: b6097712-c42e-4174-b8f2-4b1e1a5bbb3d

Inputs:

Name	Description	Type	Default Value
message	Message to print to the screen	string	Hello from Atomic Red Team test T1140!
encoded_file	File to temporarily save encoded text	path	/tmp/T1140.encoded

Attack Commands: Run with `sh`!

ENCODED=$(echo '#{message}' | b64encode -r -)
printf $ENCODED | b64decode -r
echo $ENCODED | b64decode -r
echo $(echo $ENCODED) | b64decode -r
echo $ENCODED > #{encoded_file} && b64encode -r #{encoded_file}
echo $ENCODED > #{encoded_file} && b64decode -r < #{encoded_file}
echo $ENCODED > #{encoded_file} && cat #{encoded_file} | b64decode -r
echo $ENCODED > #{encoded_file} && cat < #{encoded_file} | b64decode -r

Atomic Test #7 - FreeBSD b64encode Shebang in CLI

Using b64decode shell scripts that have Shebang in them. This is commonly how attackers obfuscate passing and executing a shell script. Seen here by TrendMicro, as well as LinPEAS. Also a there is a great Sigma rule here for it.

Supported Platforms: Linux

auto_generated_guid: 18ee2002-66e8-4518-87c5-c0ec9c8299ac

Inputs:

Name	Description	Type	Default Value
bash_encoded	Encoded	string	IyEvYmluL2Jhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
dash_encoded	Encoded	string	IyEvYmluL2Rhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
fish_encoded	Encoded	string	IyEvYmluL2Rhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
sh_encoded	Encoded	string	IyEvYmluL3NoCmVjaG8gImh0dHBzOi8vd3d3LnlvdXR1YmUuY29tL0BhdG9taWNzb25hZnJpZGF5IEZUVyIK

Attack Commands: Run with `sh`!

echo #{bash_encoded} | b64decode -r | sh
echo #{dash_encoded} | b64decode -r | sh
echo #{fish_encoded} | b64decode -r | sh
echo #{sh_encoded} | b64decode -r | sh

Dependencies: Run with `sh`!

Description: b64decode must be present

Check Prereq Commands:

which b64decode

Get Prereq Commands:

echo "please install b64decode"

Atomic Test #8 - Hex decoding with shell utilities

Use common shell utilities to decode a hex-encoded text string and echo it to the console

Supported Platforms: Linux, macOS

auto_generated_guid: 005943f9-8dd5-4349-8b46-0313c0a9f973

Inputs:

Name	Description	Type	Default Value
message	Message to print to the screen	string	Hello from Atomic Red Team test T1140!
encoded_file	File to temporarily save encoded text	path	/tmp/T1140.encoded

Attack Commands: Run with `sh`!

ENCODED=$(echo '#{message}' | xxd -ps -c 256)
printf $ENCODED | xxd -r -p
echo $ENCODED | xxd -r -p
echo $(echo $ENCODED) | xxd -r -p
echo $ENCODED > #{encoded_file} && xxd -r -p #{encoded_file}
echo $ENCODED > #{encoded_file} && xxd -r -p < #{encoded_file}
echo $ENCODED > #{encoded_file} && cat #{encoded_file} | xxd -r -p
echo $ENCODED > #{encoded_file} && cat < #{encoded_file} | xxd -r -p

Dependencies: Run with `sh`!

Description: xxd must be present

Check Prereq Commands:

which xxd

Get Prereq Commands:

echo "Please install xxd"

Atomic Test #9 - Linux Base64 Encoded Shebang in CLI

Using Linux Base64 Encoded shell scripts that have Shebang in them. This is commonly how attackers obfuscate passing and executing a shell script. Seen here by TrendMicro, as well as LinPEAS. Also a there is a great Sigma rule here for it.

Supported Platforms: Linux, macOS

auto_generated_guid: 3a15c372-67c1-4430-ac8e-ec06d641ce4d

Inputs:

Name	Description	Type	Default Value
bash_encoded	Encoded	string	IyEvYmluL2Jhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
dash_encoded	Encoded	string	IyEvYmluL2Rhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
fish_encoded	Encoded	string	IyEvYmluL2Rhc2gKZWNobyAiaHR0cHM6Ly93d3cueW91dHViZS5jb20vQGF0b21pY3NvbmFmcmlkYXkgRlRXIgo=
sh_encoded	Encoded	string	IyEvYmluL3NoCmVjaG8gImh0dHBzOi8vd3d3LnlvdXR1YmUuY29tL0BhdG9taWNzb25hZnJpZGF5IEZUVyIK

Attack Commands: Run with `sh`!

echo #{bash_encoded} | base64 -d | bash
echo #{dash_encoded} | base64 -d | bash
echo #{fish_encoded} | base64 -d | bash
echo #{sh_encoded} | base64 -d | bash

Dependencies: Run with `sh`!

Description: base64 must be present

Check Prereq Commands:

which base64

Get Prereq Commands:

echo "please install base64"

Atomic Test #10 - XOR decoding and command execution using Python

An adversary can obfuscate malicious commands or payloads using XOR and execute them on the victim's machine. This test uses Python to decode and execute commands on the machine.

Supported Platforms: Linux, macOS

auto_generated_guid: c3b65cd5-ee51-4e98-b6a3-6cbdec138efc

Inputs:

Name	Description	Type	Default Value
xor_key	Key used to decrypt the command	string	waEHleblxiQjoxFJQaIMLdHKz
encrypted_command	Encrypted command that will be executed	string	AAkqKQEM

Attack Commands: Run with `bash`!

python3 -c 'import base64; import subprocess; xor_decrypt = lambda text, key: "".join([chr(c ^ ord(k)) for c, k in zip(base64.b64decode(text.encode()), key)]); command = "#{encrypted_command}"; key = "#{xor_key}"; exec = xor_decrypt(command, key); subprocess.call(exec, shell=True)'

which python3

Get Prereq Commands:

echo "Install Python3"

Atomic Test #11 - Expand CAB with expand.exe

Uses expand.exe to extract a file from a CAB created locally. This simulates adversarial use of expand on cabinet archives. Upon success, art-expand-source.txt is extracted next to the CAB.

Supported Platforms: Windows

auto_generated_guid: 9f8b1c54-cb76-4d5e-bb1f-2f5c0e8f5a11

Inputs:

Name	Description	Type	Default Value
cab_path	Path to the CAB to expand (created if missing)	path	%TEMP%\art-expand-test.cab
output_dir	Destination directory	path	%TEMP%\art-expand-out

Attack Commands: Run with `command_prompt`!

mkdir "#{output_dir}" >nul 2>&1
echo hello from atomic red team > "PathToAtomicsFolder\T1140\src\art-expand-source.txt"
makecab "PathToAtomicsFolder\T1140\src\art-expand-source.txt" "#{cab_path}"
pushd "#{output_dir}"
expand "#{cab_path}" -F:* .
popd

Cleanup Commands:

del "PathToAtomicsFolder\T1140\src\art-expand-source.txt" >nul 2>&1
del "#{cab_path}" >nul 2>&1
rmdir "#{output_dir}" /s /q >nul 2>&1

T1140

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