Pyrogenic Infostealer static analysis – Part 0x1

Pyrogenic is heavily obfuscated Java based Infostealer which is quiet active based on ANY.RUN submission. This will be three part blog series, this post will focus on Pyrogenic static analysis, next part 0x2 we learn unpacking using Java agent and in the last part 0x3 we find similarity between Qealler/Pyrogenic variants based on static code analysis . You may download the BankPaymAdviceVend_LLCRep.jar from ANY.RUN (MD5: F0E21C7789CD57EEBF8ECDB9FADAB26B) and follow along or download the latest Qealler sample from ANY.RUN submission.

CONTENTS
  1. Overview
  2. Quick dynamic analysis
  3. Packed Pyrogenic static analysis
  4. Conclusion
  5. References

Overview

It’s currently targeting different regions e.g. Australian companies[1], Africa and the Middle East[2] based on the references. I will be using Bytecode Viewer to decompile Jar using FernFlower Java Decompiler. Let’s start with quick dynamic analysis. Our main goal for the blog series is to unpack this jar so we can analyse the capability and compare it with Qealler.

Quick Dynamic Analysis

  • Connect to CC 157.245.160[.]150 at port 80 and create the below process.
    cmd.exe /c chcp 1252 > NUL & powershell.exe -ExecutionPolicy Bypass -NoExit -NoProfile -Command -
  • Drop these two clean files sqlitejdbc.dll (MD5: a4e510d903f05892d77741c5f4d95b5d) and jnidispatch.dll (MD5: d2f0da769204b8c45c207d8f3d8fc37e) but it deletes these two file before exiting.
  • Connect to bot.whatismyipaddress.com to get public IP of the infected system.
  • Steal credential from different applications

Packed Pyrogenic static analysis

  1. Open the jar file in BCV (Bytecode Viewer), you will see multiple class files in different packages. Below pic show the main entry point of jar file.
  2. For this sample, I found out that FernFlower decompiled the source code correctly. Select View -> Pane 1 -> FernFlower -> Java in BCV as shown below.
  3. If you browse the different class files in BCV, you will find many encrypted class files which doesn’t translate to Java src code. e.g. one of them is shown below
  4. Based on the above encrypted class file, you can guess that there should be some decryption algorithm used to decrypt those files.
  5. Decryption algorithm can be custom or well known e.g. AES. Study this example java code [3] which encrypt/decrypt using AES.  Some of the keyword mentioned in the above java code e.g. getInstance can help us to find the encryption algorithm and doFinal can point to final decryption result.
  6. Let’s search for AES references after importing the decompiled src code to Eclipse IDE.


  7. Based on above images which shows multiple references, we can confirm that this sample uses the algo “AES/ECB/PKCS5Padding” and key may be  generated using “PBKDF2WithHmacSHA1” . So it confirmed that it doesn’t uses any custom decryption algorithm.
  8. We can add our code to write the data to file after doFinal call and execute the sample in IDE to get the dumped class file  Then we can decompile the class file using BCV and continue analysis. But it can be multiple layer obfuscation which can make our analysis harder and slower.

Conclusion

This above static analysis method to find the encryption routine and interesting point for breakpoint (doFinal) while debugging is very useful in Java Malware analysis. Using this approach you will not miss any code path but this require more time and effort. So in upcoming part 0x2 , we will unpack this malware using Java agent which will speed up our analysis. Hope you enjoyed the post, please share your suggestions/feedbacks or contact me on Twitter, Happy Reversing 🙂.

References

  1. NEW PYROGENIC JAR-BASED MALWARE CAMPAIGN
  2. Pyrogenic – The JAR-Based Malware Spreading Across Africa and the Middle East
  3. Java AES Encryption Decryption Example

Related Posts

2 Comments. Leave new

Leave a Reply

Your email address will not be published. Required fields are marked *

Fill out this field
Fill out this field
Please enter a valid email address.

Menu