The Cdxx virus is ransomware of the STOP/Djvu family. This malware is known for file encryption and extortion. When the Cdxx infects a computer, it targets various types of files, like documents, videos, photos, and more. It changes the file structure and adds the “.cdxx” extension to each file, making them inaccessible and unusable without the decryptor.
Cdxx Virus Overview
Cdxx
🤔 Cdxx malware can be classified as ransomware that originates from the DJVU/STOP ransomware family. Its primary purpose is to lock files that are important to you. Then, this ransomware asks its victims to pay the ransom – ($999 – $1999) in Bitcoin.
The Cdxx virus is a malware type that encrypts your files and coerces you into paying for their decryption. This ransomware encrypts various file types. Encrypted files are identifiable by a distinct “.cdxx” extension. The files touched by ransomware become impossible to access and use.
Subsequently, the ransomware demands a ransom payment in Bitcoin from its victims, ranging from $999 to $1999. In all cases, a text file with ransom payment guidances is named as “_readme.txt“.
Cdxx Ransomware operates by Salsa20 encryption algorithms to scramble the contents of the targeted files. Since Cdxx virus employs such a robust encryption method, it becomes particularly difficult, if even possible, to find the decryption key without the assistance of the attackers.
Once Cdxx malware finishes the encryption, it shows a ransom note to the victim, asking for a ransom payment for the decryption key. The ransom note contains instructions on the ways of making the payment and also often includes threats of data loss or increased ransom amounts if the demands are not met within a specified timeframe.
I have created a comprehensive list of the solutions, advice, and practices to neutralize the Cdxx ransomware and recover your files. There are situations when it may be feasible to restore your files, but sometimes, it may be impossible.
📌 Important Note!
It is critical to note that paying the ransom does not guarantee the successful files recovery. The rascals who stand behind the Cdxx virus are not trustworthy. There were the cases where people have paid the ransom, only to be denied by the cyber criminals with the decryption key provision.
Cdxx employs a unique key for every victim, with one exception:
- If Cdxx fails to connect the command and control server (C2) before starting the encryption process, it uses offline keys as a fallback option. An offline key is the same for all users, which allows for the decryption of files encrypted by the ransomware.
The Cdxx virus is highly similar to other DJVU ransomware variants such as Lkhy, Cdpo, Cdwe, and Cdaz. This virus encrypts a wide range of common file types and appends its distinct “.cdxx” extension to all files. For instance, a file named “1.jpg” would be altered to “1.jpg.cdxx” and “2.png” to “2.png.cdxx“.
Upon successful encryption, malware spawns a special text file named “_readme.txt” and places it in every folder containing the encrypted files. It as well adds this file to the desktop, so the user will not miss the attack even without opening folders.
The image below provides a visual representation of files with the “cdxx” extension:
Encrypted Files by STOP/DJVU Ransomware
| Name | Cdxx Virus |
| Ransomware family1 | DJVU/STOP2 ransomware |
| Extension | .cdxx |
| Ransomware note | _readme.txt |
| Ransom | From $999 to $1999 (in Bitcoins) |
| Contact | [email protected], [email protected] |
| Detection | Backdoor:Win32/Xtrat.B, Ransom:Win32/Mazedec.TA!MSR, Picsys.Worm.Bot.DDS |
| Symptoms |
|
| Fix Tool |
To remove possible malware infections, scan your PC:
6-day free trial available. |
This message asking payment is for restore files via decryption key:
_readme.txt (STOP/DJVU Ransomware) – The terrifying notification requesting users to pay off the ransom to unlock the encrypted data contains these annoying admonitions.
Cdxx ransomware arrives as a set of tasks that are meant to execute different tasks on a victim’s computer. One of the primary processes being launched is winupdate.exe, a tricky process that displays a fraudulent Windows update prompt during the attack. That is needed to convince the victim that a sudden system slowdown is caused by a Windows update.
Meanwhile, the ransomware runs another process (which name commonly consists of 4 random characters) which commences scanning the computer for target files and encrypting them. Then the ransomware removes Volume Shadow Copies from the system by the following CMD command:
vssadmin.exe Delete Shadows /All /Quiet
Once removed, it becomes nearly impossible to restore the previous computer state using System Restore Points. The issue is, ransomware operators are eliminating any built-in Windows approaches that could aid the victim to recover files for free. In addition, the hackers modify the Windows HOSTS file by adding a list of domains to it and linking them to the localhost IP. As a result, the victim will see a DNS_PROBE_FINISHED_NXDOMAIN error when accessing one of the listed websites.
It has come to our attention that ransomware attempts to block websites that post various how-to guides for computer users. It is obvious that by limiting specific domains, the crooks are attempting to prevent the victim from reaching relevant and helpful ransomware-attack-related information online. Malware also keeps two text files on the victim’s computer that present attack-related details – the victim’s public encryption key and personal ID. These two files are named bowsakkdestx.txt and PersonalID.txt.
After all these alterations, the malware doesn’t cease. Variants of STOP/DJVU have a tendency to install Vidar password-stealing Trojan on compromised systems. This threat has an large list of capabilities, including:
- Infiltrating the victim’s computer with malware and executing it to gain unauthorized access.
- Obtaining unauthorized access to login credentials of Steam, Telegram, and Skype.
- Manipulating and viewing files on the victim’s computer without their knowledge.
- Stealing cryptocurrency wallets from the victim’s system.
- Granting the hackers remote control over the victim’s computer for various malicious activities.
- Extracting sensitive information such as browser cookies, saved passwords, and browsing history.
The cryptography algorithm in STOP/Djvu ransomware is AES-256. So, once your data is encrypted with an online decryption key, the possibility to get your files back without paying the ransom are quite low. Thing is, the key is unique for each victim, and brute forcing it will take too much time.
Getting the online key in another way is also nearly impossible. It is kept on a command server owned by the criminals who spread the Cdxx malware. For receiving decrypting code the payment should be $1999. To obtain the payment details, the victims should contact the hackers by email ([email protected]).
The message by the ransomware states the following information:
ATTENTION! Don't worry, you can return all your files! All your files like pictures, databases, documents and other important are encrypted with strongest encryption and unique key. The only method of recovering files is to purchase decrypt tool and unique key for you. This software will decrypt all your encrypted files. What guarantees you have? You can send one of your encrypted file from your PC and we decrypt it for free. But we can decrypt only 1 file for free. File must not contain valuable information. You can get and look video overview decrypt tool: https://we.tl/t-FCWSCsjEWS Price of private key and decrypt software is $1999. Discount 50% available if you contact us first 72 hours, that's price for you is $999. Please note that you'll never restore your data without payment. Check your e-mail "Spam" or "Junk" folder if you don't get answer more than 6 hours. To get this software you need write on our e-mail: [email protected] Reserve e-mail address to contact us: [email protected] Your personal ID: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
How To Remove STOP/Djvu Ransomware?
Video Guide
How To Decrypt .cdxx Files?
How to restore big files?
Try removing .cdxx extension on a few big files and opening them. This malware has issues with large file encryption. Either the virus scanned and did not lock the file, or it failed and did not add the filemarker. If your files are very large (2GB+), the latter is most likely. Please, let me know in the comments if that will work for you.
The newest extensions were released around the end of August 2019 after the criminals made changes. This includes Cdtt, Cdpo, Cdwe etc.
As an outcome of the changes made by the criminals, STOPDecrypter is no longer supported. It has been replaced with the Emsisoft Decryptor for STOP Djvu Ransomware developed by Emsisoft.
You can download free decryption tool here: Decryptor for STOP Djvu.
-
Select folders for decryption.
Based on the default configurations, the decryptor will by default choose the accessible directories to decrypt the currently reachable drives (the connected ones), including the network drives. Additional (optional) locations can be selected with the aid of the “Add” button.
Decryptors usually propose several options depending on the specific malware family. The present possible options are displayed in the Options tab and can be enabled or turned off there. You may locate a comprehensive list of the currently active Options below.
-
Click on the “Decrypt” button.
As soon as you add all the desired locations for decryption to the list, click on the “Decrypt” button to initiate the decryption procedure.
Note that the main screen may turn you to a status view, letting you know of the active process and the decryption statistics of your data:
The decryptor will notify you once the decryption procedure is completed. If you need the report for your papers, you can save it by choosing the “Save log” button. Note that it is also possible to copy it directly to your clipboard and paste it into emails or messages here if you need to do so.
The Emsisoft Decryptor might display different messages after a failed attempt to restore your files:
✓ Error: Unable to decrypt file with ID: [your ID]
Emsisoft failed to find a corresponding decryption key in their database.
✓ No key for New Variant online ID: [your ID]
Notice: this ID appears to be an online ID, decryption is impossible
Malware uses an online key to cipher your files. There is no one to share the decryption key with you. Recovery of files without paying the criminals is impossible. 🙁
✓ Result: No key for new variant offline ID: [example ID]
This ID appears to be an offline ID. Decryption may be possible in the future.
Malware used an offline key, but files could not be restored (the offline decryption key isn’t available yet). But, this message is good news for you, since it is possible to restore your files in the future. 🙂
It can take a few weeks or months until the decryption key gets found and uploaded to the decryptor. Please follow updates regarding the decryptable DJVU versions here.
✓ Remote name could not be resolved
This stands for a DNS issue present in your system. Consider resetting your HOSTS file to default.
How to Restore .cdxx Files?
In some cases ransomware is not doom for your files…
The Cdxx ransomware encryption mechanism is next: it ciphers every file byte-by-byte, then saves a file copy, deleting (not overriding!) the original file. Thus, the data of the file location on the disk drive is lost, but the original file is not removed from the physical disk. The cell, or the sector where this file was stored, can still keep this file, but it is not present in the file system and can be overwritten by data that has been loaded to this disk after the removal. Hence, it is possible to recover your files using special software.
Anyway, after realizing it was an online algorithm, it was impossible to retrieve my encrypted files. I also had my backup drive plugged in at the time of the virus, and this was also infected, or so I thought. Every folder within my backup drive had been infected and was encrypted. However, despite losing some important files, I retrieved almost 80% of my 2TB storage.
When I started going through the folders, I noticed the readme.txt ransom note in every folder. I opened some of the folders and found that all files that were not in a subfolder within that folder had been encrypted. However, I found a flaw and a glimmer of hope when I went into the subfolders in other folders and found that these files had not been encrypted. Every folder within my c and d drives, including subfolders, had been encrypted, but this was not the case with the backup drive. Having subfolders created within a folder has saved 80% of my data.
As I said, I believe this to be only a small loophole on a backup drive. I’ve since found a further 10 % of my data on another hard drive on a different PC. So my advice is if you use a backup drive, create subfolders. I was lucky, I guess. But I was also unlucky that the virus hit as I was transferring some files from my backup.
Hopefully, this can help some other people in my situation.
Jamie NewlandRecovering your files with PhotoRec
PhotoRec is a free open-source program, which is initially created for data recovery from damaged disks, or data recovery in case they are unintentionally deleted. However, with time flow, this program adopted the ability to restore the files of 400 different file types. Hence, it can be used for data recovery after the Cdxx attack.
First, you need to download this app. It is 100% free, but the developer notifies you that there is no guarantee that your files will be retrieved. PhotoRec is distributed together with another utility of the same developer – TestDisk. The program archive will bear the TestDisk name but don’t worry. PhotoRec files are right inside.
To run PhotoRec, find and open “qphotorec_win.exe” file. No installation is required – this program has all the files it needs within the archive, hence, you can mount it on your USB drive, and help your friends/parents/anyone who has been attacked by Cdxx ransomware.
Upon the start, you will encounter the screen showing you the complete list of your disk drives. However, this information is probably irrelevant, because the required menu is placed a bit higher. Click this menu, then choose the disk which was attacked by ransomware.
After picking the disk, you need to pick the destination folder for the retrieved files. This menu is located at the lower part of the PhotoRec window. The best choice is to export them on a USB drive or any other type of removable disk.
Then, you need to indicate the file formats. This setting is located at the bottom, too. As it was mentioned, PhotoRec can regain the files in about 400 different formats.
Finally, you can initiate file recovery by pressing the “Search” button. You will see the screen where the outcomes of the scan and recovery are shown.
Cdxx files recovery Video Guide.
Frequently Asked Questions
I need your help to share this article.
It is your turn to help others. I have written this guide to help people like you. You can use the buttons below to share this on your favorite social media Facebook, Twitter, or Reddit.
Brendan SmithReferences
German 
Japanese 
Spanish 
Portuguese (Brazil) 
French 
Turkish 
Chinese (Traditional) 
Korean 
Indonesian 
Hindi 
Italian
Leave a Comment