Pierluigi Paganini July 02, 2019

A new Ransomware appeared in the threat landscape, the malware began to threats the digital world. This time using a nice but scary name: LooCipher.

Introduction

A new Ransomware began to threats the digital world. This time using a nice but scary name: LooCipher. The name is at the same time an allusion to its capabilities (thank to the term “Cipher”) and to the popular religious figure, Lucifer. Despite its evocative nickname, the functionalities of this malware are pretty straight forward, not very different from those belonging to many other ransomware families, but digging into its internals we also found elements suggesting its operators could be able to run large scale campaigns.  

Technical Analysis

Unlike most ransomware, LooCipher uses a macro-weaponized document as dropper of the real threat. We identified two different document files involved to deploy the ransomware, they are called: “Info_BSV_2019.docm” and “Info_Project_BSV_2019.docm”. Both files are very poor in design and contain a single text line inviting the user to enable macro execution.

Exploring the content in-depth, we retrieved its minimal macro code payload: its only purpose is to download the ransomware from the “hxxp://hcwyo5rfapkytajg.onion[.]pet/2hq68vxr3f.exe” dropurl and launch it.

The author did not care to obfuscate in any sophisticated way his malicious code, even some comment strings like “//binary” and “//overwrite” are still visible.

Once run, it starts the encryption of all the victim’s files, except for the system and programs folders: “Program Files”, “Program Files (x86)”, “Windows”. Obviously, this trick allows to avoid the corruption of the files needed to start the operating system, letting the user login to its PC to see the ransom request. 

After a long files enumeration phase, the ransomware encrypts all files ending with the following extensions:

During the encryption phase, for each file to be encrypted, the malware creates the encrypted copy of the files but it does not delete the original ones, rather it empties them and forces a 0-byte size.

It is not clear if this mechanism derives from buggy code or it is a specific peculiarity of this malware, intentionally introduced by the author.

When the encryption phase ends, it creates a FAQ folder within victim’s desktop reporting the instructions to proceed with ransom payment in a “friendly” Q&A form.

As stated in the payment instruction file, the victim has only five days to proceed with the payment. After this period, the key will be automatically destroyed, preventing any way to recover the user content. Similar information is also displayed in the image set as background and into the interactive pop-up window. 

As soon as the encryption phase is ended, the malicious process contacts its C2 sending information about the infected machine and retrieving the BTC address to display in the pop-up window. 

The C2 is hosted in the TOR Network, at the “hxxp://hcwyo5rfapkytajg[.]onion” address, so the malware uses some services which act as proxies between the Darknet and clearnet to easily perform its malicious actions, avoiding the installation of TOR libraries on the victim machine. The abused services are:

• https://onion.pet
• https://darknet.to/
• https://onion.sh/
• http://tor2web.xyz/

The request sent by the malware includes information like the User-ID assigned to the victim machine during the encryption phase “u=rEui7jhIJk6SaRTyhL08N7h1Sft” and its public IP address “i=xxx.xxx.xxx.xxx”. The C2 server replies specifying the BTC Address the user will pay the requested amount to, for instance “BTC_ADDR: 16HDCwCuy2R5b7YFCmsidXzHQrvHmT7VHGG”.

We noticed that every time the ransomware contacts its C2 at the “k.php” resource, the server generates a new BTC Address. Probably, the backend embeds a BTC wallet factory able to register a new wallet on the blockchain for each ransomware infection. This trick surely allows to make more stealthy BTC transactions, avoiding a huge number of transactions towards the same wallet and hardening the cash flow reconstruction. In the following table we inserted some of the BTC addresses generated by the C2:

Table. Example of Generated BTC Addresses

However, if the victim machine is offline the ransomware is not able to download the BTC address to display in the window. For this reason, the malware also embeds a fallback addresses list to use when it fails to reach the C2.

Table. Hardcoded BTC Addresses on sample

An interesting peculiarity of this ransomware is its capability to work both as encryptor and as decryptor. The last answer of the instruction file, in fact, reports that the decryptor software is embedded into the ransomware binary in order to make the decryption process as simple as possible.

In fact, after the payment the victim can click on “Check Payment” button included in the pop-up window, and so, if the transaction has been confirmed, the “DECRYPT” button will be enabled. Moreover, if the user accidentally closes the pop-up window needed to trigger the decryption, he can download a new copy of the ransomware and use it as decryptor. That copy is hosted on the MEGA repository “hxxps://mega [.nz/#!KclRVIRY!YrUgGjvldsoTuNZbCOjebAz5La7hbB41nJHk1mlgqZo”.

Clicking the “Check Payment” button, the process sends a new HTTP request to its C2 to “/d.php” in order to check if the payment related to the specific User-ID has been received.

In the specific case, the server replies with the “0” value, indicating the payment has not been approved, so the “DECRYPT” button will not be enabled. Moreover, if the contacted server is down, the malware tries to reach its TOR C2 using one of the other above-mentioned proxies, avoiding proxy service failures. 

Conclusion

In the nowadays, Ransomware is one of the quickest ways to monetize cyber-criminal activities, and for this reason a wide-range of threat actors, including micro cyber-criminals, leverage these “tools” to threaten organizations and companies. LooCipher is a new entry in this sector: it’s a Ransomware family spreading through malicious emails embedding infected Office documents, differently from the recent Sodinokibi campaign that used redirectors to land the victims on Exploit Kits infected pages (eg RIG EK).

LooCipher encrypts all files on victim computer, it abuses Clearnet-to-Tor proxy services to connect to its Command and Control hidden behind onion sites. Cybaze-Yoroi ZLAB advises to always keep a recent, tested and offline backup of all the business critical data.

Technical details, including IoCs and Yara Rules, are available in the analysis published in the Yoroi blog.

https://blog.yoroi.company/research/loocipher-the-new-infernal-ransomware/

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Pierluigi Paganini

(SecurityAffairs – loocipher, ransomware)

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