Intel — CraftedSignal Threat Feed

Persistence via Windows Installer (Msiexec)

hello@craftedsignal.io — Thu, 05 Sep 2024 14:17:05 +0000

The Windows Installer (msiexec.exe) is a legitimate system tool used for installing, updating, and removing software on Windows systems. Adversaries can abuse msiexec.exe to establish persistence mechanisms by creating malicious scheduled tasks or modifying registry run keys. This allows them to execute arbitrary code during system startup or user logon. This technique is attractive to attackers due to msiexec.exe being a trusted Windows binary, potentially evading detection by security solutions that focus on flagging unknown or suspicious processes. The use of msiexec.exe for persistence can be difficult to detect without specific monitoring rules, as it is a common and legitimate system process. This activity can be observed across various Windows versions and is frequently integrated into automated attack frameworks and scripts.

Attack Chain

An attacker gains initial access to a compromised system, potentially through phishing, exploitation of a vulnerability, or stolen credentials.
The attacker leverages msiexec.exe to create a new scheduled task using the schtasks.exe command, setting it to execute a malicious script or binary.
Alternatively, the attacker uses msiexec.exe in conjunction with reg.exe or PowerShell to modify registry keys under HKLM\Software\Microsoft\Windows\CurrentVersion\Run or HKCU\Software\Microsoft\Windows\CurrentVersion\Run, adding a pointer to their malicious executable.
The created scheduled task or registry entry points to a malicious payload, such as a reverse shell or a downloader.
The system is restarted, or the user logs on, triggering the execution of the newly created scheduled task or the malicious binary through the modified registry run key.
The malicious payload executes, establishing a persistent foothold for the attacker on the compromised system.
The attacker can now perform further actions, such as data exfiltration, lateral movement, or deployment of ransomware.

Impact

Successful exploitation allows the adversary to maintain persistent access to the compromised system. This can lead to data theft, system compromise, deployment of ransomware, or use of the system as a staging point for further attacks within the network. A single compromised system can be used to pivot and compromise additional systems, leading to a widespread security breach. The impact can include financial losses, reputational damage, and disruption of business operations.

Recommendation

Monitor process creation events for msiexec.exe spawning schtasks.exe or reg.exe to create scheduled tasks or modify registry run keys (reference: rules in this brief).
Implement and tune the Sigma rules provided in this brief to detect suspicious msiexec.exe activity related to persistence mechanisms.
Review and audit existing scheduled tasks and registry run keys for any suspicious entries or anomalies.
Enable file integrity monitoring (FIM) on critical system directories, including the Windows Task Scheduler directory and registry run key locations (reference: event.category == “file” and file.path … and event.category == “registry” and registry.path … in the rule query).
Implement application control policies to restrict the execution of unauthorized or unknown executables (reference: rule query).

Process Execution from Suspicious Windows Directories

hello@craftedsignal.io — Thu, 04 Jan 2024 12:00:00 +0000

This detection identifies process execution from suspicious default Windows directories. Attackers may hide malware in trusted paths to evade defenses, making it difficult for analysts to distinguish between legitimate and malicious activity. The detection focuses on identifying processes running from directories like C:\PerfLogs, C:\Users\Public, and various Windows subdirectories (e.g., C:\Windows\Tasks, C:\Windows\AppReadiness), where executable files are not typically expected to reside. The detection excludes known legitimate processes like SpeechUXWiz.exe, SystemSettings.exe, TrustedInstaller.exe and other Intel and IBM executables to reduce false positives. This technique is often used to bypass security controls or take advantage of existing exceptions applied to these directories. This activity was observed being used by threat actors in the Siestagraph campaign.

Attack Chain

An attacker gains initial access to the system (e.g., through phishing or exploiting a vulnerability).
The attacker drops a malicious executable into a suspicious directory like C:\Users\Public or C:\Windows\Tasks.
The attacker executes the malware from the unusual directory. This might be achieved using cmd.exe or powershell.exe.
The executed malware establishes persistence by creating a scheduled task or modifying registry keys.
The malware connects to a command-and-control (C2) server to receive further instructions.
The C2 server instructs the malware to perform reconnaissance on the network.
The malware attempts to move laterally to other systems on the network using techniques like pass-the-hash or exploiting vulnerabilities.
The attacker achieves their objective, such as data exfiltration, ransomware deployment, or establishing long-term access to the network.

Impact

Successful exploitation can lead to the execution of arbitrary code, persistence on the system, and further compromise of the network. Attackers can use this technique to bypass security controls and evade detection, potentially leading to data breaches, financial loss, or disruption of services. While the rule itself has a medium severity, the impact of a successful attack using this technique can be severe, depending on the attacker’s objectives and the compromised data.

Recommendation

Deploy the Sigma rule “Process Execution from Unusual Directory” to your SIEM and tune for your environment to detect suspicious process execution.
Investigate any alerts generated by the Sigma rule to determine if the process execution is legitimate or malicious.
Enable process creation logging, specifically Event ID 4688 with command line process auditing, to ensure the Sigma rule has the necessary data to function effectively.
Review and harden permissions on the listed suspicious directories to prevent unauthorized file creation and execution.
Block execution of unsigned or untrusted executables from these directories using application control solutions.

LSASS Loading Suspicious DLL

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

The Local Security Authority Subsystem Service (LSASS) is a critical Windows component that manages security policies and user authentication. Attackers often target LSASS to dump credentials, using techniques like injecting malicious DLLs. This detection focuses on identifying instances where LSASS loads a DLL that is either unsigned or not signed by a trusted vendor. The rule excludes known legitimate signatures and file hashes to reduce false positives. This activity is a strong indicator of credential access attempts, potentially leading to further compromise of the system and network. The signatures identified in the rule contain well-known software vendors like Microsoft, McAfee and Citrix.

Attack Chain

An attacker gains initial access to the system through various means (e.g., phishing, exploiting a vulnerability).
The attacker elevates privileges to gain sufficient access to interact with the LSASS process.
The attacker drops a malicious DLL onto the system, often disguised as a legitimate file.
The attacker injects the malicious DLL into the LSASS process using techniques like Reflective DLL Injection.
LSASS loads the injected DLL, granting the attacker access to sensitive credentials stored in memory.
The malicious DLL dumps credentials, such as plaintext passwords or NTLM hashes.
The attacker uses the stolen credentials for lateral movement to other systems on the network.
The attacker achieves their final objective, such as data exfiltration or deploying ransomware.

Impact

Successful exploitation leads to credential compromise, allowing attackers to move laterally within the network, access sensitive data, and potentially achieve complete domain dominance. This can result in data breaches, financial losses, and reputational damage. The impact depends on the level of access associated with the compromised credentials.

Recommendation

Deploy the LSASS Loading Untrusted DLL Sigma rule to your SIEM to detect suspicious DLLs loaded by LSASS.
Investigate any alerts generated by the Sigma rule and review the loaded DLL’s code signature and hash.
Block the identified SHA256 hashes listed in the IOC table to prevent the execution of known malicious DLLs.
Implement application whitelisting to restrict which DLLs can be loaded into LSASS.
Enable Sysmon process creation and image load logging to provide the necessary data for detection.