What is a rootkit?

Rootkit malware conceals itself deep within operating systems and disrupts monitoring tools. This makes eradication complex and highlights the need for robust rootkit prevention strategies.

Following infection, rootkits execute a range of actions. Depending on the attacker's goals, rootkits can launch distributed denial-of-service (DDoS) attacks, record keystrokes and user activity, extract sensitive data, or steal user credentials.

How does a rootkit work?

Rootkit malware targets security vulnerabilities and modifies operating system settings.

Threat actors deliver malware via code injection, external devices, or phishing emails. Malicious software executes automatically when users click on links or plug in USB devices. This installs the rootkit and initiates attacks.

The next phase in rootkit attacks is escalating administrative privileges. Kernel vulnerabilities enable system-wide access, while other methods hijack trusted application processes. Rootkits may also use their privileged position to run pass-the-hash operations and steal credentials.

Following privilege escalation, the rootkit establishes a persistent presence on the victim's network via kernel-mode or user-mode techniques. Malware modifies system settings so that it executes on start-up - integrating the rootkit into normal system processes.

Now, rootkits can operate in the background, stealing data and monitoring network activity. Operations often persist for months or even years. During that period, the rootkit conceals its activity by disabling security tools, running API calls, and modifying kernel data.

Types of rootkits

There are many ways to install rootkits, and rootkit attacks also implement different operational techniques.

Firmware rootkits

Firmware rootkits attack the software that runs hardware components. This is a powerful technique as firmware runs below the level of conventional operating systems. By infecting firmware, attackers can operate below the radar and make it tough to detect rootkits.

Targets of firmware attacks include hard drives and BIOS chips on workstations, routers, and network servers. Criminals can flash malware to these devices via physical methods (e.g., USB drives). However, firmware attacks typically exploit flawed update processes to deliver infected patches.

Bootloader rootkits

Bootloader rootkits target device start-up procedures by infecting the code that launches operating systems. Attackers can deliver them physically via compact discs, USB drives, DVDs, or external hard drives. Target devices automatically detect physical devices and execute rootkit malware as part of normal start-up processes.

Bootloader rootkits replace legitimate booting software (such as GRUB for Linux or Microsoft's Windows Boot Manager) with a malicious alternative. Rootkits modify kernel settings and load into the system's memory sector while the device boots.

This style of rootkit is exceptionally powerful because it executes before security tools can respond. Advanced bootloader rootkits conceal their modifications before security diagnostics can detect any changes. This makes rootkit detection and removal a complicated task.

Memory rootkits

Memory rootkits target random access memory (RAM). These types of rootkits load into the system's memory by hijacking legitimate kernel processes. When embedded in RAM, rootkits can steal credentials or data directly from memory and open backdoors for other attack vectors.

Memory rootkits are short-lived. Malware disappears from RAM when the system shuts down or reboots. However, these rootkits are highly elusive and hard to detect. Malware barely interacts with operating systems or discs and leaves few traces for security professionals to detect.

Moreover, memory-based rootkits often compromise performance by consuming resources, making removal a high priority.

Application rootkits

Application-based rootkits hijack and modify system apps, creating a malicious imitation of legitimate versions. The rootkit executes every time users open infected apps and provides access for threat actors while the application remains open.

Applications infected by rootkits run normally. For example, rootkits can infect Microsoft Office apps without betraying their presence. Users may type confidential messages, share intellectual property, or enter financial data into compromised spreadsheets.

Rootkits may hinder detection by a technique called API hooking. This technique intercepts system calls and modifies them to aid concealment (for instance, by changing the list of active processes).

Security teams can often detect rootkits embedded in applications via antivirus tools. However, camouflage techniques make these rootkits tough adversaries.

Hypervisor rootkits

These advanced rootkits infect virtual machines, creating a critical security threat to cloud environments. Hypervisor rootkits create spoofed virtual machine monitors underneath an operating system, then run the legitimate operating system on the fake hypervisor.

Kernel mode rootkits

The kernel is the most privileged and powerful level of an operating system. Users with kernel mode privileges can access and modify virtually all system components, including network hardware, memory, and software assets.

Kernel-mode rootkits exploit this privileged position. These types of rootkits load themselves into kernels disguised as modules and drivers. When implanted, rootkits modify kernel settings and intercept system calls to cover their tracks.

Rootkits operating deep within the kernel are hard to detect and potentially highly damaging. Even poorly-coded malware can compromise network performance, while flawless rootkits provide extensive access to data and system configurations.

User-mode rootkits

User-mode rootkits do not penetrate deep within operating system kernels. Instead, these rootkits exploit user privileges to access and control applications or devices. This makes user-mode kits less powerful but simpler to deploy than kernel-based tools.

User-mode kits employ APP hooking to conceal their activity. They also use a technique called DLL injection to coerce legitimate applications into running malicious code.

How to detect a rootkit?

Rootkits aim to evade countermeasures. However, security teams can detect rootkits with the right techniques and tools.

The most important tool in your arsenal is a rootkit scan. Rootkit scanning tools look for the signatures of known rootkit agents - the footprints left behind when rootkits infiltrate networks and conceal their activities.

Signatures include many data points, but focus on the distinctive memory instructions executed by rootkits. Researchers analyze rootkit agents in quarantined environments to extract code strings and behavior patterns. With enough detail, they can build accurate profiles for active rootkit variants.

Signatures aren't the only available rootkit detection technique. Advanced solutions also scan for characteristic rootkit behavior. Scanners compare network activity with secure baselines. They correlate outputs with known rootkit behavior, potentially delivering early warning to network managers.

Behavioral analysis helps catch sophisticated polymorphic rootkits that change their form to evade detection. They are also better equipped to detect rootkits that reside deep within system memory.

Analysts can also pair behavior analysis with memory and firmware integrity checks. These tools check for suspicious signs of code injection, kernel changes, or bootloader modifications, providing extra assurance against stealthy rootkit attacks.

What to do if you detect a rootkit?

If you suspect a device has a rootkit infection, don't turn it on as normal. Instead, use Windows Safe Mode to access the operating system. This boots Windows with a skeleton portfolio of drivers and services - enough to run diagnostics while shrinking the attack surface for malware agents.

Safe Mode can even expose rootkit attacks by starving them of resources and limiting access to system apps. To access Safe Mode, press F8 during start-up and choose Safe Mode from the menu that appears.

Disconnect infected devices from the wider network, back up data on all devices that may be exposed, and engage scanning tools to assess the extent of the attack. In many cases, network security tools can eradicate the agent. However, OS installs and even BIOS wipes may also be required.

How to prevent a rootkit?

If your systems fall victim to rootkit attacks, detection and removal are both complex and uncertain. While investing in detection tools is vital, prevention strategies minimize the risk of infection. Here are some reliable rootkit prevention and risk management tips:

Train staff to cut phishing risks

Many rootkit attacks start when an employee clicks a seemingly innocent link in a phishing email. Unfortunately, we can't totally safeguard networks against human error. However, companies should train staff to spot malicious phishing emails.

Ensure team members understand how phishers work, spotting spoofed sender addresses, and why it is unwise to download unrequested attachments or click embedded links. Refresh phishing training annually, as awareness is usually temporary.

Phishing is not the only important staff training theme. Educate staff to avoid shadow IT installations (for example, unapproved browser extensions or free VPN apps).

Implement patch management policies

Rootkit attacks often gain access to target networks via application exploits (software vulnerabilities that allow code injection and malware delivery).

Most vendors fix vulnerabilities following detection. However, security teams can lag behind vendor updates. Even short delays open the door to exploit attacks. Patching internet-facing apps is critically important.

Security teams must also monitor software lifecycles. Vendors may stop updating applications at the end of their life cycle, increasing their vulnerability to rootkit attacks. This applies to operating systems, firmware, and collaboration tools.

Harden system configurations

Generally speaking, minimal configurations cut the risk of rootkit infections and make containment easier. Disable unused ports to reduce the attack surface and remove unnecessary services on workplace devices.

Use application allowlisting

Application allowlisting enforces strict policies about what processes applications can execute. Only enable authorized processes and block unknown executables before your security team can assess and approve them.

Employ reliable threat detection solutions

Antivirus or antimalware tools catch less sophisticated rootkit types before they cause harm. They are particularly effective when protecting apps against rootkit infection, but struggle against memory or bootloader rootkits. Source advanced tools that combine signature and behavioral detection, but never rely solely on threat detection solutions.

Filter inbound and outbound traffic

Firewalls provide another layer of defense against all forms of malware, including rootkits. Next-generation firewalls use Deep Packet Inspection to analyze traffic for rootkit signatures, blocking cyber threats before they reach network endpoints.

Block hidden threats with rootkit prevention measures

Rootkits implant themselves deep within operating systems and applications, using concealment techniques to evade detection. Left undetected, these hidden cyber threats can steal data and credentials, compromise performance, and take down hardware or web services.

Companies need effective rootkit prevention and detection strategies. Train staff, strengthen firewalls, scan for intrusions, and patch software to cut infection risks. And implement advanced scanning tools to detect successful infections.