Researchers from Menlo Security recently discovered that unknown attackers have carried out a series of attacks on government agencies in the Asia-Pacific region and North America. The PureCrypter malware used in these attacks is capable of delivering several types of ransomware and information thieves to the victim's computer at once.
“The malware campaign delivered several types of malware, including Redline Stealer, AgentTesla, Eternity, Blackmoon, and Philadelphia Ransomware,” the researchers said.
PureCrypter is a .NET-based malware loader that first went public in March 2021. Its operator leases the bootloader to other cybercriminals to distribute various types of malware.
When activated, PureCrypter delivers a payload from a C2 server, which in the last reported attack was a compromised server of an unnamed non-profit organization.
The sample the Menlo Security researchers analyzed is called AgentTesla. When launched, it establishes a connection to a Pakistani FTP server, which is used to store the stolen data.
AgentTesla is a .NET malware family that has been used by cybercriminals for the past eight years. The peak of his "popularity" came at the end of 2020 - the beginning of 2021.
A recent Cofense report highlights that despite its age, AgentTesla remains a cost-effective and high-performance backdoor that has been constantly developed and improved over the years. AgentTesla keylogger activity accounts for roughly a third of all keylogger reports registered by Cofense Intelligence in 2022.
Malware capabilities include the following:
- registration of keystrokes of the victim to collect confidential information;
- stealing passwords stored in web browsers, email or FTP clients;
- creating screenshots of the desktop;
- interception of data from the clipboard;
- exfiltrating stolen data to a C2 server via FTP or SMTP.
In attacks studied by Menlo Security, it was found that hackers used a "process hollowing" technique to inject the AgentTesla payload into a legitimate process ("cvtres.exe") to avoid detection by antivirus tools. In addition, AgentTesla uses XOR encryption to secure communication with the C2 server.
Menlo Security believes that the attackers behind the PureCrypter campaign aren't a big deal, but it's worth keeping an eye on their activities due to their focus on government agencies.
It is likely that attackers will continue to use the compromised infrastructure for as long as possible before switching to a new one.