Suspicious PowerShell Script Using Cryptography Namespace

hello@craftedsignal.io — Wed, 03 Jan 2024 18:00:00 +0000

This threat brief focuses on detecting suspicious PowerShell activity involving the System.Security.Cryptography namespace, excluding common hashing algorithms like SHA and MD5. The detection leverages Windows PowerShell Script Block Logging (EventCode 4104) to identify scripts using cryptographic functions. This is significant because malware often uses cryptography to decrypt or decode additional malicious payloads, which can lead to further code execution, privilege escalation, or persistence within the compromised environment. The technique is commonly used by malware families like AsyncRAT, XWorm, and VIP Keylogger. Defenders should investigate the parent process of such scripts, the decrypted data, network connections established by the script, and the user context in which the script is executed.

Attack Chain

An attacker gains initial access to a system, possibly through phishing or exploiting a vulnerability.
The attacker executes a PowerShell script on the compromised system.
The PowerShell script utilizes the System.Security.Cryptography namespace to perform cryptographic operations.
The script decrypts or decodes a malicious payload (e.g., a second-stage executable or configuration file).
The decrypted payload is written to disk or loaded directly into memory.
The attacker executes the decrypted payload, potentially establishing persistence via registry keys or scheduled tasks.
The malware leverages the established persistence mechanism for long-term access.
The attacker performs malicious actions such as data exfiltration, lateral movement, or remote command execution.

Impact

Successful exploitation allows attackers to bypass security measures by hiding malicious code within encrypted payloads. This can lead to data theft, system compromise, and further propagation within the network. Malware families like AsyncRAT, XWorm, and VIP Keylogger use this technique to maintain persistence and perform malicious activities undetected. The impact can range from individual workstation compromise to large-scale data breaches depending on the attacker’s objectives and the compromised system’s role within the organization.

Recommendation

Enable PowerShell Script Block Logging on all endpoints to generate the necessary logs (EventCode 4104) for detection.
Deploy the Sigma rule Detect Suspicious PowerShell Cryptography Namespace Usage to your SIEM to detect the described activity.
Investigate any alerts generated by the Sigma rule by examining the parent process, decrypted data, network connections, and the user executing the script.
Review and tune the Sigma rule Detect Suspicious PowerShell Cryptography Namespace Usage based on your environment’s specific needs and known-good PowerShell usage to reduce false positives.
Implement application control policies to restrict the execution of unsigned or untrusted PowerShell scripts.

Braodo Stealer Screen Capture in TEMP Directory

hello@craftedsignal.io — Wed, 03 Jan 2024 10:00:00 +0000

The Braodo stealer malware is known for capturing screenshots of a victim’s desktop as part of its data theft activities. This malware, often distributed through malicious campaigns, targets sensitive information by creating image files of the user’s active screen. These screenshots are typically saved in directories that are easily accessible and commonly used by malware, such as temporary folders. This technique allows attackers to gather credentials, financial information, or other confidential data displayed on the screen. The stealer has been observed in campaigns originating from Vietnam, targeting users in the United States with malware, fraud, and dropshipping schemes. Detecting and responding to these types of screen capture attempts is crucial for preventing sensitive data from being compromised and exfiltrated.

Attack Chain

The user unknowingly downloads and executes a malicious file, potentially delivered through a phishing email or drive-by download.
The Braodo stealer malware is executed on the victim’s system.
The malware begins capturing screenshots of the victim’s desktop using Windows APIs.
The screenshots are saved as .png, .jpg, or .bmp files.
The files are saved in the user’s TEMP directory (e.g., C:\Users\\AppData\Local\Temp\).
The malware may compress or encrypt the captured screenshots.
The malware exfiltrates the captured data to a command-and-control server.
The attacker gains access to sensitive information displayed on the victim’s screen, such as credentials or financial data, and uses it for malicious purposes.

Impact

Successful exploitation can lead to the theft of sensitive information, including credentials, financial data, and personally identifiable information (PII). This can result in financial loss, identity theft, and reputational damage for the victim. The Braodo stealer has been observed targeting users in the United States, indicating a broad scope of potential victims. The malware’s ability to capture screenshots allows attackers to bypass multi-factor authentication and other security measures that rely on information displayed on the screen.

Recommendation

Enable Sysmon Event ID 11 (FileCreate) logging to monitor file creation events on endpoints (required for the Sigma rules below).
Deploy the provided Sigma rule Detect Screen Capture Files Created in TEMP Directory to identify potential screen capture activity in temporary directories.
Investigate any alerts generated by the Sigma rule, focusing on processes creating image files in the TEMP directory.
Review and update endpoint security policies to prevent the execution of malware from temporary directories.
Monitor network traffic for suspicious outbound connections from processes creating screen capture files (T1071).

Vip-Keylogger — CraftedSignal Threat Feed

Suspicious PowerShell Script Using Cryptography Namespace

Attack Chain

Impact

Recommendation

Braodo Stealer Screen Capture in TEMP Directory

Attack Chain

Impact

Recommendation