Agent Tesla Malware Uses Multi-Stage Attacks with PowerShell Scripts

Researchers from Palo Alto Networks have uncovered a series of malicious spam campaigns leveraging the notorious Agent Tesla malware through intricate, multi-stage infection vectors.

The attack begins innocuously enough with the receipt of a socially engineered email, often crafted to appear legitimate and relevant to the recipient.

These emails carry an archive attachment, which typically contains a JavaScript (JS) file.

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This file, when executed, sets off the initial stage of the infection by downloading a PowerShell script.

The Role of PowerShell in Multi-Stage Attacks

PowerShell scripts have become a favored tool for cybercriminals due to their ability to bypass traditional security measures and execute commands directly in memory, evading detection by anti-virus software.

This particular campaign utilizes PowerShell to deliver and execute the next payload, the Agent Tesla malware.

The script is designed to drop and execute the final executables directly into system memory, circumventing traditional file-based detection methods.

Furthermore, the malware injects itself into a legitimate running process to further mask its malicious activities.

To combat this threat, Symantec has updated its detection signatures and applied several strategies:

• Adaptive-based Signatures: Signatures like ACM.Ps-CPE!g2 and ACM.Wscr-CNPE!g1 are designed to identify and block script-based attacks, particularly those involving PowerShell and Wscript.
• Behavior-based Detection: Symantec employs SONAR technology that flags suspicious behaviors, such as unusual process launches or network connections, helping to catch the malware in action.
• File-based Detection: Signatures like ISB.Dropper!gen1 and Trojan.Gen.2 are used to identify known malicious files associated with the Agent Tesla campaign.
• Network-based Monitoring: Network audits focus on scripting host processes making connections, ensuring that communications from suspicious scripts are intercepted and scrutinized.
• Web-based Protection: WebPulse-enabled products from Symantec cover and block observed domains/IPs associated with the campaign, preventing further downloads or connections.

VMware Carbon Black also enhances defenses against this malware by recommending blocking all forms of malware, including known, suspect, and potentially unwanted programs (PUPs).

Additionally, there’s a delay in execution for cloud scans, allowing time for the system to query VMware Carbon Black Cloud’s reputation service for real-time threat information.

According to the Report, The increasing sophistication of these attacks, utilizing tools like PowerShell, underlines the need for comprehensive security strategies that not only focus on file-based threats but also on behavior, scripts, and network activities.

Organizations are advised to update their security measures, especially those related to email filtering, script execution, and endpoint protection, to mitigate the risks posed by such advanced persistent threats.

Moreover, regular security training for employees to recognize and handle suspicious emails can be crucial in preventing the initial stage of infection.

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