Pierluigi Paganini January 29, 2018

Security researchers from ESET have tied another family of ransomware, dubbed FriedEx (aka BitPaymer), to the authors of the Dridex Trojan.

The Dridex banking Trojan that has been around since 2014, it was involved in numerous campaigns against financial institutions over the years and crooks have continuously improved it.

In April 2017, millions of people were targeted by a phishing campaign exploiting a Microsoft Word 0day and aimed to spread the Dridex Banking Trojan, a few days ago security researchers at Forcepoint spotted a new spam campaign that is abusing compromised FTP servers as a repository for malicious documents and infecting users with the Dridex banking Trojan.

Now, security researchers from ESET have tied another strain of ransomware, dubbed FriedEx (aka BitPaymer), to the authors of the Dridex Trojan.

FriedEx was first spotted in July, and in August it was responsible for infections at NHS hospitals in Scotland.

The FriedEx ransomware was involved in attacks against high profile targets, researchers believe it was delivered via Remote Desktop Protocol (RDP) brute force attacks.

The ransomware encrypts each file using a randomly generated RC4 key that is then encrypted with a hardcoded 1024-bit RSA public key.

“Initially dubbed BitPaymer, based on text in its ransom demand web site, this ransomware was discovered in early July 2017 by Michael Gillespie. In August, it returned to the spotlight and made headlines by infecting NHS hospitals in Scotland.” states the analysis published by ESET.

“FriedEx focuses on higher profile targets and companies rather than regular end users and is usually delivered via an RDP brute force attack. The ransomware encrypts each file with a randomly generated RC4 key, which is then encrypted using the hardcoded 1024-bit RSA public key and saved in the corresponding .readme_txt file.”

The analysis of FriedEx code revealed that many similarities with Dridex code.

For example, the Dridex and FriedEx binaries share the same portion of a function used for generating UserID, the experts also noticed that the order of the functions in the binaries is the same in both malware families, a circumstance that suggests the two malware share the same codebase.

“It resolves all system API calls on the fly by searching for them by hash, stores all strings in encrypted form, looks up registry keys and values by hash, etc. The resulting binary is very low profile in terms of static features and it’s very hard to tell what the malware is doing without a deeper analysis.” states ESET.

Both Dridex and FriedEx use the same packer, but experts explained that the same packer is also used by other malware families like QBot, Emotet or Ursnif also use it.

Another similarity discovered by the researchers is related to the PDB (Program Database) paths included in both malware. PDB paths point to a file that contains debug symbols used by vxers to identify crashes, the paths revealed the binaries of both threats are compiled in Visual Studio 2015.

The experts also analyzed the timestamps of the binaries and discovered in many cases they had the same date of compilation, but it is not a coincidence.

“Not only do the compilations with the same date have time differences of several minutes at most (which implies Dridex guys probably compile both projects concurrently), but the randomly generated constants are also identical in these samples. These constants change with each compilation as a form of polymorphism, to make the analysis harder and to help avoid detection.” continues the analysis.

The experts concluded that FriedEx was developed by the Dridex development team, they believe that the criminal gang not only will continue to improve the banking Trojan but it will also follow malware “trends” developing their own strain of ransomware.

Pierluigi Paganini

(Security Affairs – FriedEx ransomware, Dridex)

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