Cybercriminals are constantly devising new email campaigns for distributing malware. These campaigns usually impersonate a trusted entity and advise the email recipient about a pressing issue that requires immediate attention. The emails often have an attached file that must be opened to find out further information about the issue detailed in the email.

One recently detected campaign impersonates travel service providers such as and advises the recipient about a problem with a recent booking. One of the intercepted emails explains that an error has occurred with a booking that has resulted in a double charge to the user’s credit card which requires immediate attention. The email has a PDF attachment which needs to be opened for further information. PDF files are increasingly being used in email campaigns for distributing malware. The PDF files often contain a script that generates an error message when the file is opened that tells the user that the content of the file cannot be displayed, and they are provided with an option to download the file.

In this campaign, the PDF file contains a script that generates a fake popup message. If clicked, a connection is made to a malicious URL and a download of an obfuscated JavaScript file is initiated. The script downloads the next stage PowerShell payload, and on execution, drops a malicious DLL file on the device. The DLL file searches for certain critical system processes and attempts to forcibly stop them, makes changes to the registry that affect the Windows Antimalware Scan Interface (AMSI) and ensures that the malware is executed without being detected by security solutions. An analysis of the DLL file by researchers at Forcepoint shows the file is from the Agent Tesla malware family. Agent Tesla is a remote access trojan (RAT) that first appeared in 2014 and grew in popularity during the COVID-19 pandemic. Agent Tesla is provided under the malware-as-a-service model and is popular with initial access brokers, who specialize in gaining access to devices and accounts and then sell that access to other cybercriminals such as ransomware gangs.

Agent Tesla allows commands to be run on compromised systems and is capable of stealing sensitive information, such as login credentials stored in browsers. The malware can also take screenshots, log keystrokes, and perform other malicious actions. The malware uses multiple layers of obfuscation to ensure it is not detected by antivirus solutions. The malware is commonly used to gain initial access to business networks, primarily through phishing campaigns. In this campaign, by impersonating a popular travel service company there is a reasonable chance that the user may have used the service in the past or have a current booking and will therefore open the email. However, since the emails reference a charge to a credit card, that may be sufficient to get the user to open the attachment.

To protect against this and other malware distribution campaigns, businesses should ensure that they protect all endpoints with email security and antivirus solutions that are capable of behavioral analysis of files, as Agent Tesla and many other popular malware variants use obfuscation to bypass signature-based security solutions. Web filtering solutions provide added protection as they block connections to the malicious URLs that host malware and they can be configured to block downloads of executable files from the Internet. It is also important to provide security awareness training to the workforce to raise awareness of cyber threats and conduct phishing simulations to test the effectiveness of training.

TitanHQ offers a range of cybersecurity solutions for businesses and managed service providers to help them defend against cyber threats delivered via email and the Internet, including spam filtering with email sandboxing, web filtering, and security awareness training. Give the team a call today to find out more about improving your defenses against phishing and malware. All TitanHQ solutions are available on a free trial to allow you to test the products and see for yourself the difference they make.