T1140 - Deobfuscate/Decode Files or Information

Description from ATT&CK

Adversaries may use [Obfuscated Files or Information](https://attack.mitre.org/techniques/T1027) 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](https://attack.mitre.org/software/S0160) 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 command to reassemble binary fragments into a malicious payload.(Citation: Carbon Black Obfuscation Sept 2016) Sometimes a user's action may be required to open it for deobfuscation or decryption as part of [User Execution](https://attack.mitre.org/techniques/T1204). 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

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 
1

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 
1

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 
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sh
!

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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 
1

sh
!

Description: Python must be present
Check Prereq Commands:
1

which python3
Get Prereq Commands:
1

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 
1

sh
!

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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 
1

sh
!

Description: Perl must be present
Check Prereq Commands:
1

which perl
Get Prereq Commands:
1

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 
1

sh
!

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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 
1

sh
!

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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 
1

sh
!

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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 
1

sh
!

Description: b64decode must be present
Check Prereq Commands:
1

which b64decode
Get Prereq Commands:
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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 
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sh
!

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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 
1

sh
!

Description: xxd must be present
Check Prereq Commands:
1

which xxd
Get Prereq Commands:
1

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 
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sh
!

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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 
1

sh
!

Description: base64 must be present
Check Prereq Commands:
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which base64
Get Prereq Commands:
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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 
1

bash
!

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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)'

Dependencies: Run with 
1

bash
!

Description: Python3 must be installed
Check Prereq Commands:
1

which python3
Get Prereq Commands:
1

echo "Install Python3"