Linux ransomware already infected at least tens of users

Pierluigi Paganini November 07, 2015

Researchers at Russian antivirus company Doctor Web have discovered a Linux ransomware that has already infected tens of users.

Ransomware is a profitable instrument in the criminal ecosystem, security experts discover new variant on a weekly basis. This week the new variant of Cryptowall, the Cryptowall 4.0, appeared in the wild, meanwhile an offline ransomware is targeting Russian users.

News of the day is that researchers at Russian antivirus company Doctor Web have spotted a new file-encrypting ransomware, dubbed Linux.Encoder.1, that is targeting Linux systems. It has been estimated that tens of users have already fallen victim to this Linux ransomware.

“Doctor Web warns users about new encryption ransomware targeting Linux operating systems. Judging from the directories in which the Trojan encrypts files, one can draw a conclusion that the main target of cybercriminals is website administrators whose machines have web servers deployed on. Doctor Web security researchers presume that at least tens of users have already fallen victim to this Trojan.” states the blog post published by Doctor Web.

The Linux ransomware is written in C and leverages the PolarSSL library, it launches itself as a daemon that encrypt data and deletes the original files from the system

Linux ransomware ransom demand

The Linux ransomware requires administrator privileges in order to work, once a machine is infected by the threat, the malware downloads the files containing attackers’ demands and a file containing the path to a public RSA key. The Linux ransomware is launched as a daemon and deletes the original files, subsequently, the RSA key is used to store AES keys used to encrypt files.

“First, Linux.Encoder.1 encrypts all files in home directories and directories related to website administration. Then the Trojan recursively traverses the whole file system starting with the directory from which it is launched; next time, starting with a root directory (“/”). At that, the Trojan encrypts only files with specified extensions and only if a directory name starts with one of the strings indicated by cybercriminals.” continues the post.

“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.

In order to recover the encrypted files, victims are asked to pay one Bitcoin (roughly $380 at today’s rate), once the ransom is paid the files are decrypted using a private RSA key that retrieves the AES key from encrypted files.

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Pierluigi Paganini

(Security Affairs –Linux ransomware, cybercrime)

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