Understanding Persistence Techniques in Penetration Testing
Why Persistence Matters
Maintaining access to a system after gaining initial entry is crucial for attackers. Initial access is often short-lived and fragile. Systems are rebooted, users log out, credentials are rotated, and security controls are updated. Any of these actions can immediately break an attacker’s foothold if no persistence mechanism exists.
If defenders reboot the system or apply security measures, persistence techniques allow continued control. These techniques rely on legitimate operating system features that automatically execute code under specific conditions such as startup, login, or scheduled events. Because these mechanisms are part of normal system behavior, they often blend into the environment and evade casual inspection.
Persistence also enables attackers to operate efficiently. Rather than repeatedly exploiting the same vulnerability, attackers can focus on post-exploitation activities such as credential harvesting, lateral movement, data collection, and long-term monitoring. This extended dwell time significantly increases the impact of a compromise.
From a defensive perspective, persistence is frequently what separates a contained incident from a sustained breach. Many organizations successfully remediate the initial exploit while leaving persistence mechanisms intact. Understanding how persistence works is essential to fully removing an attacker from an environment.
There are several ways to achieve persistence, each with unique advantages depending on reliability, privilege level, visibility, and the target environment.
Common Methods of Persistence
Windows Services
Windows services run in the background without requiring user interaction, making them a reliable choice for persistence. Attackers can install a malicious service configured to start automatically at boot.
Services are commonly used by legitimate software, which makes malicious services difficult to distinguish from normal system activity. When named to resemble system or vendor components, they often evade user suspicion.
Why Services Are Effective:
Start at boot without user action
Run continuously in the background
Can execute with SYSTEM privileges
Use Case: Attackers create a disguised service to maintain persistent access with elevated privileges, even if the user logs out or the system restarts.
Once installed, a service can provide consistent execution regardless of user behavior, making it one of the most stable persistence techniques on Windows systems.
Scheduled Tasks
Windows Task Scheduler enables the automation of tasks, which can be leveraged for persistence. Tasks can be configured to run at specific times or in response to system events.
Example Command:
schtasks /create /tn "UpdateService" /sc onlogon /tr "malicious.exe"Key options:
Execution frequency:
MINUTE,HOURLY,DAILY,WEEKLY,MONTHLY,ONCETrigger events:
ONSTART,ONLOGON,ONIDLEPrivilege escalation: Can run as
SYSTEMfor higher access levelsUse Case: Attackers schedule a hidden task that runs at every login to maintain access without user interaction.
Scheduled tasks ensure execution at defined intervals or system events, making them an effective method. Tasks can also be configured to delay execution or run under specific conditions, reducing their visibility to users and defenders.
WMI Event Consumers
Windows Management Instrumentation (WMI) allows attackers to create event-based persistence by triggering actions based on system events rather than fixed schedules.
This approach does not rely on files being placed in startup locations or obvious configuration changes, which increases stealth.
Why WMI is Useful for Persistence:
Runs with SYSTEM privileges
Can trigger execution based on system events
Difficult to detect using conventional security tools
Use Case: Attackers create a WMI event subscription that executes a payload whenever a specific system event occurs, such as a user logging in or a network connection being established.
Because WMI subscriptions are stored within the WMI repository, they are often overlooked during incident response and remain active long after initial access is removed.
Registry Modifications
The Windows registry is a key location for attackers to maintain access. Since it stores configuration details for the OS and applications, it can be manipulated to automatically execute malicious code.
Registry-based persistence is simple to implement and supported by default Windows behavior, making it a common technique.
Notable Registry Keys for Persistence:
- Run and RunOnce Keys:
HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\RunHKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce- Use Case: Attackers place malicious scripts here to execute every time the user logs in, ensuring continued access.
- CMD AutoRun Key:
HKCU\Software\Microsoft\Command Processor\AutoRun- Use Case: A command-line script is configured to run each time CMD.EXE is launched, allowing attackers to execute commands persistently.
- HKCU Load Key:
HKCU\Software\Microsoft\Windows NT\CurrentVersion\Windows- Use Case: Attackers leverage this key to load a malicious executable whenever the user logs in, often bypassing security tools that focus on startup folders or registry Run keys.
These keys allow automatic execution of commands at login or system startup and are frequently abused due to their reliability.
Startup Folder Exploitation
Another approach that avoids registry modifications is placing malicious files in the startup directory. Any executable, script, or link in this folder runs automatically when the user logs in.
Location:
%AppData%\Microsoft\Windows\Start Menu\Programs\Startup- Use Case: Attackers drop a payload in this folder to execute malware whenever the user logs in, ensuring persistence across reboots.
This technique is straightforward and effective, particularly in environments where users have write access to their own profiles.
It is especially useful in virtual desktop or shared workstation environments where user sessions are frequently reset, ensuring execution each time a new session begins.
DLL Search Order Hijacking
Many Windows applications load dynamic-link libraries without specifying an absolute path. When this occurs, Windows searches for the required DLL using a predefined search order. Attackers can exploit this behavior by placing a malicious DLL in a location that is searched before the legitimate DLL.
This technique does not rely on explicit startup mechanisms such as services or scheduled tasks. Instead, it abuses normal application execution, making it less obvious and harder to attribute to persistence.
Why DLL Hijacking Is Effective:
Executes when a legitimate application is launched
Does not require registry changes or scheduled execution
Often blends into normal application behavior
Use Case: Attackers place a malicious DLL in the same directory as a trusted application. When the application starts, the malicious DLL is loaded automatically, executing attacker-controlled code.
DLL hijacking is particularly effective when paired with applications that launch at startup or login. This allows attackers to achieve persistence indirectly by relying on software the user or system already trusts.
Because the persistence mechanism is tied to application execution rather than a visible startup entry, defenders may remove malware binaries while leaving the triggering application intact, allowing the attack to reoccur.
This method is commonly observed in environments with legacy applications or poorly configured software that does not enforce secure DLL loading practices.
Conclusion
Understanding persistence techniques is essential for both attackers and defenders. Persistence often determines whether a compromise is brief or long-lasting.
While penetration testers use these methods to evaluate security postures, defenders must identify and remove persistence mechanisms to fully remediate an incident. Failing to do so allows attackers to regain access even after apparent cleanup, turning a single intrusion into a prolonged security failure.
