Windows Defender VBA Bypass

TL;DR

Windows Defender can block VBA code it deems suspicious. This guide shows simple techniques to bypass these blocks, primarily by obfuscating your code and adjusting macro settings. Warning: Bypassing security measures should only be done for legitimate testing or development purposes on systems you own or have permission to modify. Malicious use is illegal and harmful.

Steps

1. Understand the Block
   • Windows Defender uses heuristics to identify potentially malicious VBA code. Common triggers include using APIs related to file system access, registry modification, or network communication.
   • The error message usually indicates a blocked macro due to security settings or potential threats.
2. Adjust Macro Security Settings (Temporary – Use with Caution)

   This is the simplest method but significantly reduces your system’s security. Only use this for testing and revert changes immediately afterwards.

   • Open Microsoft Office application (e.g., Excel, Word).
   • Go to File > Options > Trust Center > Trust Center Settings…
   • Select Macro Settings.
   • Choose either Disable all macros with notification or Enable all macros (not recommended; potentially dangerous code can run). The first option is preferable as it allows you to choose which macros to enable.
   • Click OK and restart the application.

   Important: After testing, revert these settings back to their original values (typically ‘Disable all macros except digitally signed macros’ or similar) for security.

3. Code Obfuscation – Simple Techniques

   Obfuscation makes your code harder for Defender to recognize as malicious. These are basic techniques; more sophisticated methods exist.

   • Variable Renaming: Change variable names to meaningless characters (e.g., x, y, z).
   • String Manipulation: Split strings into multiple parts and concatenate them at runtime.

     Dim strPart1 As String
     Dim strPart2 As String
     strPart1 = "http://"
     strPart2 = "example.com"
     MsgBox strPart1 & strPart2

   • Using ASCII Codes: Represent characters using their ASCII codes.

     Sub Example()
       Dim charCode As Integer
       charCode = 72 'ASCII code for H
       Debug.Print Chr(charCode) 'Prints H
     End Sub

   • Using Mathematical Operations: Perform simple mathematical operations to hide values.

     Dim hiddenValue As Integer
     hiddenValue = 10 + 5 - 2
     MsgBox hiddenValue  'Displays 13

4. Code Obfuscation – More Advanced (but still relatively simple)
   • Using the `Instr` Function: Hide strings within other strings.

     Dim searchString As String
     Dim longString As String
     searchString = "example.com"
     longString = "This is a test string containing example.com somewhere in it." 
     If InStr(1, longString, searchString) > 0 Then
       MsgBox "Found the string!" 
     End If

   • Using `Mid` Function: Split strings and reconstruct them.

     Dim part1 As String
     Dim part2 As String
     part1 = Left("example.com", 4)
     part2 = Right("example.com", 6)
     MsgBox part1 & part2

5. Delay Execution

   Adding delays can sometimes bypass heuristics that look for immediate malicious actions.

   Sub DelayedExecution()
     Application.Wait Now + TimeValue("0:00:05") ' Wait 5 seconds
     ' Your code here
   End Sub

6. Break Up Code into Smaller Modules

   Splitting your code across multiple modules can make it harder for Defender to analyze the entire script at once.

7. Digital Signatures (Best Practice – Requires a Certificate)

   Digitally signing your VBA code is the most reliable way to bypass Defender blocks, as it verifies the source of the code. This requires purchasing a digital certificate from a trusted provider.

   • Obtain a Code Signing Certificate.
   • Sign your VBA project using the certificate in the Visual Basic Editor (VBE). Tools > Digital Signature.

Important Considerations

• False Positives: Defender may sometimes incorrectly flag legitimate code as malicious.
• Security Risks: Bypassing security measures weakens your system’s protection. Only do this on systems you control and understand the risks involved.
• cyber security software evolves constantly; techniques that work today might not work tomorrow.