Security Experts:

File-Encrypting Ransomware Targets Linux Users

Researchers at Russian antivirus company Doctor Web have come across a new file-encrypting ransomware that appears to be targeting machines running Linux operating systems.

The security firm believes tens of users have already fallen victim to the threat, which seems to be mainly aimed at webmasters whose machines host web servers.

It’s unclear at this point how the malware is distributed and installed on victims’ computers, but experts noted that the threat requires administrator privileges in order to work. Once it infects a device, the ransomware, detected by Dr. Web as Linux.Encoder.1, downloads a couple of files containing the attacker's demands and one file containing a public RSA key that is used to store the AES keys for encrypting files, Dr. Web said.

The malware, which is written in C and leverages the PolarSSL library, then launches itself as a daemon and deletes the original files.

According to researchers, the malware encrypts files stored in the home and root directories, and folders related to web servers and website administration, including /var/lib/mysql, /var/www, /etc/nginx, /etc/apache, /var/log, public_html, www, webapp, backup, .git and .svn. Linux.Encoder.1 targets web development source code, documents, applications and media files.

“To encrypt each file, the Trojan generates an AES key. After files are encrypted using AES-CBC-128, they are appended with the .encrypted extension. Into every directory that contains encrypted files, the Trojan plants a README_FOR_DECRYPT.txt file with a ransom demand,” Dr. Web explained.

Once their files are encrypted, victims are asked to pay one Bitcoin (roughly $380 at today’s rate) to get them back.

AES encryption has yet to be cracked, but Dr. Web says it’s investigating ways to recover files held hostage by this piece of ransomware. If the ransom is paid, the files are decrypted using a private RSA key that retrieves the AES key from encrypted files.

While file-encrypting ransomware often uses encryption algorithms that are impossible to break, experts might be able to obtain the keys needed to recover the lost files. Kaspersky Lab recently announced that it had recovered all 14,000 decryption keys used by CoinVault and Bitcryptor ransomware.

Related Reading: CryptoWall 4.0 Released With Filename Encryption Feature

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.