AAYU Ransomware (.aayu File Extension)

What is Aayu?

A Aayu ransomware attack is undeniably distressing. It encrypts your files and demands a ransom in Bitcoins, typically around $1000. The primary objective of the cybercriminals spreading this malware is money laundering; they are not interested in personal information or other sensitive data.

The encryption used by this virus is currently unbreakable. The challenge in decryption stems not only from the encryption method itself but also because the decryption keys are securely stored on a remote server under the control of the perpetrators. The sheer number of possible keys (2*10^78) renders brute force or any similar decryption attempts futile.

In addition to encryption, Aayu malware implements changes to several crucial system settings, complicating the search for a decryption method. It blocks the execution of installation files and restricts access to anti-malware resources online. Other alterations to system settings further degrade the usability of your PC.

Understanding how the infection occurred is vital for preventing future incidents. This virus typically proliferates via websites offering "free" versions of popular software. While downloading a pirated version of Photoshop might seem harmless, there's no guarantee that the software hasn't been tampered with to include malicious code.

Aayu Encryption process

The Aayu uses the Salsa20 encryption algorithm. That is not the strongest method, but it still provides an overwhelming amount of possible decryption keys. To brute force the 78-digit number of keys, you need 3.5 unvigintillion years (1*10^65), even if you use the most powerful regular PC. Quantum computers can show a bit better results, but it is still too slow to get your files back while you are alive.

The exact algorithm of encryption is next: malware scans each folder for the files it is able to encrypt. Then, when it finds the target, it makes a copy of your file, removes the original one, encrypts the copy and leaves it instead of the removed original. Such a procedure is done to prevent the situation when you have already opened the file, so ransomware is not able to read it because of the Windows restrictions. To each encrypted copy, the virus adds the specific extension - ".aayu". Then, ransomware creates a _readme.txt file in the folder where the encrypted file is located, and goes to the next folder.

Such an encryption method can be exploited for file recovery. Since the original file is deleted, you may try to recover it using the file recovery tools. The less time is passed - the bigger the chance to get your files back, so hurry up!

Another specific moment that can help you to use the files even after the encryption is the fact that Aayu ransomware encrypts only the first 150KB of each file. Hence, you can try to run a big file, such as video or music, without the encryption. Similar feature also works with other ransomware families - Dharma, Conti and Makop encrypt the same 150KB.

Aayu note:

Ransom note is the same for the whole STOP/DJVU family. In fact, it is one of the main signs of to which family the certain ransomware belongs. Here is the typical note for STOP/Djvu family:

External Links:

Indicators of Compromise(IOC)