Cdxx Virus Ransomware (.cdxx File)

What is Cdxx ransomware?

Seeing that your files have .cdxx extension and _readme.txt files in various folders mean that you are infected with Cdxx ransomware. This sort of malware is created to extort money from the users, previously encrypting the files on its PC. It is likely impossible to decrypt the files without special software.

Cdxx virus and any other member of the STOP/Djvu family use the Salsa20 encryption mechanism. This cipher has an enormous amount of possible decryption keys, so it is impossible to brute force them, for example. Even with quantum computers, you will likely spend more time than our planet will approximately exist. But don’t worry - using specific applications designed especially for file decryption purposes, you may get your files back in just several hours.

The main ways of Cdxx ransomware distribution are third-party websites that offer the users to get some programs for free or use different dubious tools. Hackers who break the license checking procedure in programs (this action allows them to use the program without any payments) inject malicious code, or even the whole virus, into their “products”. Malware developers pay such people.

Dubious tools are even easier to use for that purpose. Usually, they are created for outlaw actions, like generating the license keys for specific programs or activating Windows without any payments. Antivirus programs detect all such apps, so crooks always instruct you to disable your security tool or add the hack tool to the allowlist. Unfortunately, you will not understand what happens until it is too late.

Encryption process

The Cdxx ransomware 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 - ".cdxx". 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 Cdxx 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.

Ransom note: _readme.txt

Ransom note is the same for the whole ransomware 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:

🔗 HowToFix.Guide: How To Decrypt .cdxx Files?

Indicators of Compromise(IOC)

File Name	MD5	File Size
📜 SAMPLE.EXE	87ba288f14fbf826d4cf061d9f8e72ed	767488
📜 SAMPLE.EXE	d1aa460d429d1a3a7354252293cb487f	689664
📜 SAMPLE.EXE	d29a970d622c9ff06e6f89fc2a52110e	9581609
📜 SAMPLE.EXE	defd2b4b32a95284081f3fd648e78f2e	696832
📜 SAMPLE.EXE	0b31fe7345c7d6f28989c516108d53e3	641285
📜 SAMPLE.EXE	709dc9523c485bdba7b65944a010e56a	6884078
📜 SAMPLE.EXE	d73567b918afe0081de4251aec9035d3	19233710