KeyPass, a new variant of the STOP ransomware, has been detected across 20 countries in the last two weeks — and researchers still aren’t sure exactly how it spreads.

According to Kaspersky Lab, the most likely infection vector is fake installers masquerading as benign software that downloads the ransomware module. Written in C++ and compiled in Microsoft Visual Studio, this Trojan first makes a copy of its executable in LocalAppData, launches it and then deletes the file.

Next, the malware spawns multiple instances of itself and begins passing both assigned victim ID numbers and encryption keys as command line arguments. Each file receives the .KEYPASS extension and up to 5 MBs of data is encrypted. All directories receive the “!!!KEYPASS_DECRYPTION_INFO!!!.txt” ransom note, which directs victims to pay $300 within 72 hours to have their files restored.

Since Aug. 8, the ransomware has spread across 20 countries, including Brazil, Mongolia and Algeria.

Key Concerns for Corporations

As the Kaspersky researchers noted in a blog post on Securelist, “The developers of this Trojan implemented a very simplistic scheme,” using the advanced encryption standard’s symmetric AES-256 algorithm in ciphertext feedback (CFB) mode with Zero IV and identical 32-byte keys for each file. In addition, if the ransomware can’t contact its command-and-control (C&C) server, it uses a hardcoded encryption key and ID, making the decryption of any files “trivial,” according to the researchers.

Despite its obvious simplicity, however, KeyPass comes with several key concerns. First is the lack of certainty about the mechanism of infection. While the leading candidate is fake installers, possibly used for software cracks or other gray market programs, some victims claimed they were infected without downloading anything. And since the ransomware infects both local drives and network shares while avoiding specific directories, such as those for Internet Explorer or Google, users may not notice the problem until the 72-hour window for “cheap” decryption has already expired.

Also worth noting is the existence of a graphical user interface (GUI) “manual control” mode, which lets attackers alter the encryption process by changing the encryption key, editing victim IDs, modifying file extensions and managing the list of excluded paths.

How to Keep KeyPass at an Arm’s Length

Christopher Scott, chief technology officer (CTO) and global remediation lead for IBM X-Force Incident Response and Intelligence Services (IRIS), advises companies to focus on security hygiene to prevent ransomware attacks such as KeyPass. With 69 percent of organizations worried that traditional antivirus solutions won’t stop threats, according to the Ponemon Institute, security teams should “embrace endpoint detection and response (EDR) technology to detect these attacks earlier to reduce overall impact,” Scott wrote.

Sources: Securelist, Ponemon Institute