Securing Against Persistent Access: How Attackers Maintain Control and Elevate Privileges

Once attackers have gained initial access to a system, they don’t simply stop there. Their next goal is often to ensure they can return at will, evade detection, and possibly gain higher privileges or control over the system. There are various techniques attackers use to achieve these goals, and we need to understand exactly where our defenses should focus.

In this article, I’ll walk you through the techniques attackers use to maintain access and escalate privileges—and, more importantly, the steps you can take to disrupt their plans.

Persistence: Ensuring They Can Return Anytime

Persistence techniques allow attackers to maintain their foothold on compromised systems, even after reboots or updates. Here’s a look at some of the most common ways attackers ensure they have continuous access and what we can do to prevent it.

1.???? Creating New Accounts

Attackers often create new user accounts, sometimes with elevated privileges, to give themselves a backup way into the system. These accounts might look like regular users, blending in with legitimate accounts.

Regularly review and audit user accounts, especially admin-level accounts. Use automated tools to detect unusual account creation and consider setting up alerts for changes in privileged accounts.

2.???? Scheduled Tasks and Cron Jobs

By setting up scheduled tasks (Windows) or cron jobs (Linux/Unix), attackers can automate their access. These tasks allow their code or backdoor to execute at specific times, ensuring they regain control after a reboot or period of inactivity.

Regularly review scheduled tasks and cron jobs on critical systems. Limit who can create or modify these tasks and monitor for changes to detect unauthorized additions.

3.???? Registry Run Keys and Startup Items

On Windows, attackers often leverage the registry to add persistence by setting specific registry keys that run their malicious code on startup. This way, their code executes every time the system boots.

Monitor registry keys related to startup and restrict access to sensitive parts of the registry. Tools like Windows Defender or other endpoint protection platforms can detect and alert on suspicious registry modifications.

4.???? Modify Existing Services

Attackers may alter legitimate services to execute malicious payloads. By changing a service’s configuration, they can ensure that their code runs whenever that service is triggered.

Implement file integrity monitoring to detect unauthorized modifications to services. Ensure only trusted personnel have permissions to modify service configurations, and monitor for changes.

5.???? Boot and Logon Autostart Execution

Attackers sometimes modify system boot processes to launch their code as the system starts. This technique is common in sophisticated malware and ensures persistence even if security tools are installed.

Secure boot processes with boot-level protections, such as Secure Boot, and monitor for changes in startup configurations. Apply endpoint protection solutions that can detect boot-level anomalies.

Privilege Escalation: Getting Higher-Level Access

Once attackers have persistent access, they often seek to escalate privileges to gain full control. Privilege escalation allows attackers to move from a lower-level user to a privileged account, expanding their reach and enabling deeper access to sensitive data.

1.???? Exploiting Vulnerabilities in Software or OS

Attackers use exploits to target vulnerabilities in software, the OS, or services to gain admin-level access. This could involve exploiting outdated software or unpatched systems.

Regular patching is your best defense here. Ensure all systems, especially those with high-value access, are updated regularly. Use vulnerability scanning tools to keep track of unpatched vulnerabilities in your environment.

2.???? Credential Dumping

Attackers often dump credentials from memory, the registry, or configuration files to acquire passwords. Tools like Mimikatz can extract passwords from memory, allowing attackers to impersonate legitimate users.

Use least-privilege access principles and enforce strong, unique passwords. Enable multi-factor authentication (MFA) and implement protections like Windows Credential Guard to secure credentials in memory.

3.???? Pass the Hash

In Windows environments, attackers use the Pass-the-Hash technique to authenticate without knowing a user’s password, instead using the hashed password stored in memory or elsewhere.

Limit access to critical systems, and ensure privileged accounts only operate on secure systems. Use unique passwords on high-value accounts, and consider implementing network segmentation to limit movement.

4.???? Abusing Sudo and Sudoers File

On Unix-based systems, attackers can misuse sudo privileges to elevate their access. By manipulating sudo policies, attackers may gain access to commands reserved for root or admin users.

Regularly review the sudoers file and restrict access to privileged commands. Implement logging to detect any unusual or unauthorized uses of sudo.

5.???? DLL Hijacking and Injection

Attackers sometimes load malicious DLLs (Dynamic-Link Libraries) into legitimate applications to gain elevated privileges. By hijacking or injecting their code into a trusted application, they can bypass certain security controls.

Restrict write permissions to sensitive directories and monitor for unauthorized DLL loads. Application whitelisting and regular file integrity checks can further reduce the risk.

Keeping Attackers at Bay: A Proactive Defense Strategy

So, how can you put all these defenses into action? Here are some steps to create a proactive strategy that addresses both persistence and privilege escalation techniques:

1. Enforce Multi-Factor Authentication (MFA): One of the simplest and most effective measures against unauthorized access.
2. Use Endpoint Detection and Response (EDR): EDR tools monitor for suspicious activity, like unauthorized changes in scheduled tasks or unusual account creations, allowing you to respond quickly.
3. Implement the Principle of Least Privilege: Ensure users have only the access they need and regularly review account permissions. This limits the damage even if an attacker gains access.
4. Conduct Regular Audits and Patch Management: Regularly audit critical systems for new accounts, privilege levels, and software updates. Patching is crucial to prevent attackers from exploiting known vulnerabilities.
5. Educate Your Team: Human error is often a vulnerability. Regularly train staff on secure practices and how to recognize phishing, privilege misuse, or other suspicious activities.

By understanding the techniques attackers use to maintain access and escalate privileges, you’re better equipped to detect them early and prevent them from getting a permanent foothold. A proactive approach helps not only in preventing breaches but also in limiting the potential impact if an attacker manages to slip through.

With these strategies, you’re setting up a resilient defense that anticipates attackers’ next moves and works actively to counter them.