Unmasking the Python Threat: Threat Hunting for Pysa

In the world of cybersecurity, Python-based threats have been gaining traction, and one such notorious adversary is Pysa. Pysa is a malicious Python script that poses a significant risk to organizations due to its ability to execute stealthy attacks. As Pysa is designed to evade traditional security measures, the practice of proactive threat hunting becomes crucial to detect and neutralize this elusive threat. In this blog, we will explore threat hunting for Pysa, featuring real-world examples, Splunk queries, and YARA rules to help organizations bolster their defenses against this Python menace.

Pysa is a polymorphic Python script that can adapt its code to evade signature-based detection. It typically spreads through infected files, email attachments, or malicious downloads. Pysa can perform various malicious activities, including data exfiltration, remote code execution, and privilege escalation. As its presence is often subtle, organizations need to employ proactive threat hunting techniques to uncover this hidden threat.

Let’s explore practical threat hunting examples to detect and respond to Pysa malware:

Example 1: Python Script Execution
Monitor systems for any suspicious Python script execution attempts.

index=main sourcetype=”WinEventLog:Microsoft-Windows-Sysmon/Operational” EventCode=1 earliest=-1w

Look for uncommon script names or unusual patterns of Python script execution.

Example 2: Abnormal Network Activity
Hunt for unusual network connections associated with Pysa’s command-and-control (C2) communication.

index=network earliest=-1d | stats count by dest_ip

Investigate any significant spikes in outbound connections, especially to known malicious IP addresses.

YARA rules offer a powerful way to create custom signatures for detecting Pysa malware. Let’s create a YARA rule for Pysa:

rule Pysa_Malware {
meta:
description = “Detects Pysa malware scripts”
strings:
$pysa_marker = “pysa_marker” wide ascii
$pysa_marker2 = “pysa_marker2” wide ascii
$magic = { 23 21 } // Shebang for Python scripts (#!)
condition:
$magic at 0 and all of ($pysa_marker, $pysa_marker2)
}

Leverage Splunk for endpoint and network monitoring to detect potential Pysa infections:

# Endpoint Activity Monitoring
index=main sourcetype=”WinEventLog:Microsoft-Windows-Security-Auditing” EventCode=4688
| search New_Process_Name=”*.py”

# Network Activity Monitoring
index=network earliest=-1w
| rex field=_raw “Host=(?<dest_host>[^\s]+)”
| rex field=_raw “User_Agent=(?<user_agent>[^\s]+)”
| search dest_host=”*.onion” OR user_agent=”pysa_marker” OR user_agent=”pysa_marker2"

Proactive threat hunting is an essential practice in uncovering the hidden Python threat posed by Pysa. By utilizing Splunk queries and YARA rules, organizations can strengthen their detection capabilities, identify suspicious activities, and respond swiftly to Pysa malware. Continuous monitoring and staying up-to-date with threat intelligence will aid in countering this elusive adversary effectively. Implementing these strategies will fortify your organization’s cybersecurity defenses, ensuring resilience against Pysa and other Python-based threats. Remember, a vigilant and proactive approach to threat hunting is the key to outsmarting Pysa before it takes hold. Happy hunting!

(Note: The examples provided in this blog are intended for illustrative purposes only and may require customization based on the specific environment and requirements of individual organizations.)