File-Creation — CraftedSignal Threat Feed

Suspicious Alternate Data Stream (ADS) File Creation

hello@craftedsignal.io — Fri, 26 Jan 2024 18:00:00 +0000

This detection focuses on identifying the creation of Alternate Data Streams (ADS) on Windows systems, a technique often employed by adversaries to conceal malicious code or data within seemingly benign files. Attackers leverage scripting engines and command interpreters to write ADS to various file types, including executables, documents, and media files. This activity is uncommon in legitimate workflows, making it a valuable indicator of potential compromise. The rule is designed to trigger on file creation events where the process creating the file is a known script or command interpreter (cmd.exe, powershell.exe, etc.) and the target file has a suspicious extension. The detection excludes common legitimate ADS usage patterns. This technique is used for defense evasion, allowing malware to persist without being easily detected by traditional security measures.

Attack Chain

An attacker gains initial access to a Windows system (e.g., through phishing or exploiting a vulnerability).
The attacker uses a command interpreter (cmd.exe, powershell.exe, etc.) or scripting engine (wscript.exe, cscript.exe) to execute malicious code.
The malicious code creates an Alternate Data Stream (ADS) on a targeted file (e.g., an executable, document, or image). The targeted file’s extension could be pdf, dll, exe, dat, etc.
The attacker hides malicious code or data within the ADS, making it less visible to standard file system scans and security tools. The ADS is written to a file path using the C:\\*:\* syntax.
The attacker may rename or clean up any staging files to further conceal their activity.
The attacker can then execute the hidden code within the ADS, or use the ADS to store configuration data for later use.
The attacker maintains persistence by using the ADS to store and execute malicious code, bypassing typical file-based security measures.
The ultimate goal is to maintain unauthorized access to the system, potentially leading to data exfiltration, lateral movement, or other malicious activities.

Impact

Successful exploitation allows attackers to hide malicious code within legitimate files, evading detection by traditional security measures. This can lead to prolonged persistence on compromised systems, enabling data theft, ransomware deployment, or other malicious activities. While the specific number of victims is unknown, this technique is broadly applicable across Windows environments, potentially affecting a wide range of organizations.

Recommendation

Deploy the Sigma rule Suspicious ADS File Creation via Cmd to detect ADS creation events initiated by cmd.exe.
Deploy the Sigma rule Suspicious ADS File Creation via PowerShell to detect ADS creation events initiated by powershell.exe.
Enable Sysmon Event ID 15 (FileCreateStreamHash) to provide detailed information about ADS creation events, as referenced in the rule’s setup instructions.
Investigate any alerts generated by these rules, focusing on the file paths, creating processes, and command-line arguments involved, as detailed in the rule’s triage and analysis notes.

Executable or Script Creation in Temporary Paths

hello@craftedsignal.io — Wed, 03 Jan 2024 12:00:00 +0000

This threat brief focuses on the creation of executable files or scripts within temporary directories on Windows systems, a common tactic used by adversaries to bypass security controls and establish persistence. This behavior is often indicative of malicious activity, such as malware installation, privilege escalation, or unauthorized code execution. The observed activity involves writing files with extensions like .exe, .dll, .ps1, and .bat into common temporary locations like \Windows\Temp\ or \AppData\Local\Temp\. This technique allows attackers to hide malicious files among legitimate temporary files, making detection more challenging. References to campaigns like Volt Typhoon, and ransomware families like LockBit highlight the importance of detecting this behavior.

Attack Chain

The attacker gains initial access to the system (e.g., through phishing or exploiting a vulnerability).
The attacker drops a malicious executable or script onto the compromised system.
To evade detection, the malicious file is created in a temporary directory such as C:\Windows\Temp\ or C:\Users\\AppData\Local\Temp\.
The attacker uses a dropper or installer to write the malicious file (e.g., using cmd.exe, powershell.exe).
The attacker may rename the file to further disguise its purpose.
The attacker executes the malicious file, potentially leading to code execution, privilege escalation, or persistence.
The executed malware performs malicious actions, such as lateral movement, data exfiltration, or ransomware deployment.
The attacker maintains persistence on the system, ensuring continued access and control.

Impact

Successful exploitation can lead to unauthorized code execution, privilege escalation, and persistent access within the targeted environment. This can result in data theft, system compromise, or ransomware deployment. The references to campaigns like Volt Typhoon and ransomware families like LockBit highlight the potential for significant disruption and financial loss. Multiple analytic stories, such as AsyncRAT, DarkGate Malware, and Qakbot, highlight the prevalence of this technique across various threat actors.

Recommendation

Enable Sysmon EventID 11 (FileCreate) logging to monitor file creation events on endpoints.
Deploy the Sigma rule “Executable or Script Creation in Temp Path” to your SIEM and tune for your environment.
Investigate any file creation events in temporary directories involving executable or script file types (.exe, .dll, .ps1, .bat, etc.).
Review and filter events based on your organization’s normal activity to reduce false positives, as mentioned in the “known_false_positives” section of the source.
Monitor for processes spawned from temporary directories, using a process creation monitoring tool and correlate with other suspicious activities.

WScript or CScript Dropper

hello@craftedsignal.io — Tue, 02 Jan 2024 12:00:00 +0000

The WScript or CScript Dropper technique is a method employed by attackers to introduce malicious script files into a system. It leverages the built-in Windows scripting hosts, cscript.exe and wscript.exe, to write files with extensions commonly associated with scripting languages (e.g., .js, .vbs, .wsf). These scripts are often written to temporary or user-accessible directories, such as \Temp\, \AppData\, or \Startup\, where they can be executed later, either manually or…