A recently observed ransomware family is targeting Linux-based file storage systems (NAS servers) made by QNAP, Intezer’s security researchers reveal. 

Dubbed QNAPCrypt, the threat targets said NAS servers in an attempt to encrypt files on them and hold them for ransom. Currently featuring a very low detection rate, the malware is likely the work of the authors of Linux.Rex.

Intezer has discovered both ARM and x86 variants of QNAPCrypt, as well as two design flaws in the ransomware infrastructure that allowed them to temporarily stop the campaign and force the authors into deploying new instances. 

While the ransomware works similarly to other ransomware, the ransom note it delivers was included solely as a text file, without a message on the screen. The malware operators provide a different, unique Bitcoin wallet to each victim, which is fetched from the command and control server (C&C) before file encryption, along with a public RSA key. 

While analyzing the malware, the security researchers discovered that the list of Bitcoin wallets was static, being created in advance, and that the ransomware would stop its malicious operation as soon as all of the wallets in the list are allocated. 

The researchers simulated the infection of more than 1,091 victims from 15 different campaigns, which resulted in the attackers running out of unique Bitcoin wallets to supply to their victims. This forced the operators to update their implants to circumvent this design flaw, Intezer says. 

A newer variant of the malware was released after several days, featuring a significant amount of code from previous QNAPCrypt instances and Linux.Rex. The new iteration has an embedded static wallet and RSA public key.

The initial attack vector, the researchers reveal, was found to be SSH brute force. The operators mainly target NAS server providers, which explains why they have chosen to label the malware QNAPCrypt. 

The x86 variant of the ransomware was found to reuse a large portion of code from old instances of x86 Linux.Rex builds, a piece of malware known for deploying exploits against Drupal servers, to conduct ransomware and distributed denial of service (DDoS) operations.

“Unfortunately detection rates of QNAPCrypt are low, and the ransomware could create significant monetary losses and economic damage in comparison to other types of Linux threats,” Intezer concludes.