A new ransomware has been found in the wild that is currently undetected by antivirus engines on public scanning platforms. Its name is NextCry due to the extension appended to encrypted files and that it targets clients of the NextCloud file sync and share service.
The malware targets Nextcloud instances and for the time being there is no free decryption tool available for victims.
xact64, a Nextcloud user, posted some details about the malware in an attempt to find a way to decrypt personal files.
Although his system was backed up, the synchronization process had started to update files on a laptop with their encrypted version on the server. He took action the moment he saw the files renamed but some of them still got processed by NextCry, otherwise known as Next-Cry.
“I realized immediately that my server got hacked and those files got encrypted. The first thing I did was pull the server to limit the damage that was being done (only 50% of my files got encrypted)” – xact64
Looking at the malware binary, Michael Gillespie said that the threat seems new and pointed out the NextCry ransomware uses Base64 to encode the file names. The odd part is that an encrypted file’s content is also encoded this way, after first being encrypted.
The malware has not been submitted to the ID Ransomware service before but some details are available.
NextCry is a Python script compiled in a Linux ELF binary using pyInstaller. At the moment of writing, not one antivirus engine on the VirusTotal scanning platform detects it.
Nexcloud servers targeted
The ransom note is in a file named “READ_FOR_DECRYPT” stating that the data is encrypted with the AES algorithm with a 256-bit key. Gillespie confirmed that AES-256 is used and that the key is encrypted with an RSA-2048 public key embedded in the malware code.
In the analyzed sample the ransom demanded is BTC 0.025, which converts to about $210 at the moment of writing. A bitcoin wallet is provided but no transactions have been recorded until now.
Security annalist named shuum successfully extracted the compiled Python script and we can clearly see that this ransomware specifically targets NextCloud services.
When executed, the ransomware will first find the victim’s NextCloud file share and sync data directory by reading the service’s config.php file. It will then delete some folders that could be used to restore files and then encrypts all the files in the data directory.
More than one case spotted
Another Nexcloud user named Alex posted on the platform’s support page about being hit by NextCry ransomware. They say that access to their instance had been locked via SSH and ran the latest version of the software, suggesting that some vulnerability was exploited to get in. Also said that their Nextcloud installation runs on an old Linux computer with NGINX. This detail may provide the answer to how the attacker was able to get access.
“I have my own linux server (an old thin client I gave a second life) with nginx reverse-proxy” – xact64
On October 24, Nextcloud released an urgent alert about a remote code execution vulnerability that impacts the default Nextcloud NGINX configuration.
Tracked as CVE-2019-11043, the flaw is in the PHP-FPM (FastCGI Process Manager) component, included by some hosting providers like Nextcloud in their default setup. A public exploit exists and has been leveraged to compromised servers.
Nextcloud’s recommendation for administrators is to upgrade their PHP packages and NGINX configuration file to the latest version.
Nextcloud currently investigating the incidents and will provide more information as it becomes available.