Pierluigi Paganini June 12, 2017

Malware researchers at security firm Fortinet have spotted MacRansom, it is the first Mac ransomware offered as a RaaS Service.

Malware researchers at security firm Fortinet have spotted a new strain of ransomware dubbed MacRansom that targets Mac machines.

The malware is available with Ransomware-as-a-service (RaaS) model through a hidden service in the TOR network. Experts believe this is the first time a Mac ransomware is offered as RaaS.

“Just recently, we here at FortiGuard Labs discovered a Ransomware-as-a-service (RaaS) that uses a web portal hosted in a TOR network which has become a trend nowadays. However, in this case it was rather interesting to see cybercriminals attack an operating system other than Windows. And this could be the first time to see RaaS that targets Mac OS.” states the analysis published by Fortinet.

Despite the threat is not sophisticated like other similar threats it could cause serious problems to the victims because it encrypts victim’s files. The availability of  MacRansom as RaaS makes it easy to arranges ransomware campaign to crooks that have no specific skills.

MacRansom variant is not readily available through the Tor portal, would-be crooks can contact the author of the ransomware in order to receive their version of the threat.

“This MacRansom variant is not readily available through the portal. It is necessary to contact the author directly to build the ransomware. At first, we thought of it as a scam since there was no sample but to verify this we dropped the author an email and unexpectedly received a response.” continues the analysis.

MacRansom implements symmetric encryption with a hard-coded key and the ransomware only encrypts a maximum of 128 files, it demands 0.25 bitcoin (around $700) for decryption keys.

Researchers found two sets of symmetric keys used by the ransomware:

• ReadmeKey: 0x3127DE5F0F9BA796
• TargetFileKey: 0x39A622DDB50B49E9

The ReadmeKey is used to decrypt ._README_ file that contains the ransom notes and instructions, while the TargetFileKey is used to encrypt and decrypt the victim’s files.

The malicious code implements anti-analysis activity, the first thing the ransomware does is to check if the sample is being run in a non-Mac environment or if it is running in debugged environment.

The author gives 30 per cent to the Bitcoin address of the customer once the victim has paid the ransom.

Customers just have to spread the threat, for example delivering it via spam emails on through drive-by download attacks.

The author discourages drive-by download attacks or other approaches that involve uploading customized versions of MacRansom.

“It is not every day that we see new ransomware specifically targeting Mac OS platform. Even if it is far inferior from most current ransomware targeting Windows, it doesn’t fail to encrypt victim’s files or prevent access to important files, thereby causing real damage.” concluded Fortinet.

“Last but not the least, this MacRansom variant is potentially being brewed by copycats as we saw quite a lot of similar code and ideas taken from previous OSX ransomware. Even though it utilizes anti-analysis tricks, which differs from previous OSX ransomware, these are well-known techniques widely deployed by many malware authors. MacRansom is yet another example of the prevalence of the ransomware threat, regardless of the OS platform being run.”

Pierluigi Paganini

(Security Affairs – MacRansom, malware)

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