What is DLL Hijacking?

Each Windows program relies on small assistive files named DLLs (Dynamic Link Libraries). These provide applications with functionality for simple activities such as printing, saving a file, or going online. When a malicious DLL is hidden inside by a hacker with the same name, the application picks it up in secret. No pop-ups, no antivirus notice—silent command.

DLL Hijacking is an undetectable attack method has been used in nation-state intelligence operations, corporate data breaches, and ransomware epidemics—without being noticed for weeks or months. A single misplaced file can open administrator access, deploy backdoors, steal passwords, and breach entire networks.

DLL Hijacking alone in 2023 accounted for multiple advanced threats aimed at finance tools, VPN clients, antivirus applications, and even signed applications from reputed vendors such as Microsoft and Adobe.

What is DLL Hijacking?

DLL Hijacking occurs when an attacker replacing or injecting a malicious DLL file into the execution process of an application. Windows applications frequently look for DLLs in defined locations (for example, in the application directory, system folders). If the attacker puts the malicious DLL at a location where it is checked by the search path, then the application uses that file, and the code gets executed with the privileges of the application.

How DLL Hijacking Works

DLL Hijacking is the most popular technique used by hackers to trick genuine software into running malicious code.

1. Search Order Vulnerability

All Windows programs rely on .dlls—also called Dynamic Link Libraries—to execute particular features (such as printing, graphics, or network access).

When a program requires a DLL, Windows searches for it in a certain sequence, such as:

1. Application's directory
2. System32 directory
3. Windows directory
4. Current working directory
5. Paths in the PATH environment variable

Vulnerability: If the application does not provide the complete path of the necessary DLL, Windows simply loads the first one it encounters. An attacker can exploit this by putting a malicious DLL in a higher-priority directory (such as the application's directory or a shared network directory).

2. Application Trigger

Once the program executes, it goes searching for the DLL it needs—like someone searching for a device in a cluttered toolbox. If the malicious DLL has been put somewhere earlier in the search path, the app takes it up without realizing it's a fake.

There are no warnings and no antivirus notifications (unless behavior-based protection is turned on). The app is still acting as though it's employing a trusted file—despite being hijacked.

3. Payload Execution

Once the hijacked DLL has been loaded. The attacker now inside in the system. Here what happen after

• Data theft: The DLL can steal keystrokes, read from memory, or steal stored passwords.
• Privilege escalation: The malware executes with the same rights as the app. If the app is executed as admin—so is the malware.
• Backdoor installation: The DLL may quietly establish a remote access channel so the hacker can come back later.
• Lateral movement: In enterprise settings, a single hijacked DLL can enable attackers to pivot to other systems on the network.

Types of DLL Hijacking Attacks:

Mainly there are 3 types of DLL Hijacking Attacks:

1. DLL Search Order Hijacking (DLL Preloading Attack)

DLL Search Order Hijacking targets how Windows goes looking for and loading DLL files. At startup for the program, it goes looking for required DLLs in a specific sequence—from the app folder locally first, before checking the system folders. If a malicious DLL with the same name exists in the app’s folder, Windows loads it first.

Example: A program loads version of .dll. Instead of loading the safe one in C:\\\\Windows\\\\System32, it checks its own directory first. If an attacker places a malicious version of .dll there, the bad file gets loaded. It is dangerous because:

• Runs with the same amount of privileges as the application (even admin, if escalated).
• Does not involve modifying the real software.
• Can be employed to load backdoors, keyloggers, or spyware without being detected.

2. DLL Side-Loading Attack

DLL Side-Loading exploits how trusted software (often from large vendors) loads DLLs from relative paths. Attackers trick these applications into loading a malicious DLL that is disguised to look legitimate—especially when located in the same folder or a trusted directory.

Targeted Directory: Most side-loading attacks abused the WinSxS (Windows Side-by-Side) directory. This directory holds multiple versions of shared DLLs to support multiple applications.

Example: An attacker deploys a malicious DLL in addition to a signed executable (e.g., from Adobe or Microsoft). When the signed application runs, it unknowingly loads the malicious DLL, providing attackers with an open door without raising alarms from antivirus software. It is dangerous because:

• Avoids trust verification because it is used by signed applications.
• Exploits vendor software trust.
• Used usually in Advanced Persistent Threats (APT) and state-sponsored attacks.

3. Phantom DLL Hijacking

Phantom DLL Hijacking occurs when an application keeps trying to load a DLL that no longer exists—maybe it was deleted or renamed. The attackers monitor these failed loads of the DLL and place a dummy DLL with the expected name in the directory. The next time the app is executed, it loads the malicious DLL successfully.

Example: An application tries to load abc.dll that was removed years before. The attacker places a fake abc.dll at the correct location, and the application makes use of it without knowing. It is dangerous because:

• Targets software with outdated or lingering dependencies.
• Functions even on patched systems if missing DLL call is not updated.
• Hard to find because no actual vulnerability exists—just a logic bug in the application.

Steps to Find Missing DLL

In the case of DLL Hijacking attack, attackers trick Windows programs to load malicious versions of DLLs in place of the original DLLs. It is achievable if an application is not able to locate the supposed Dynamic Link Library (DLL) file and loads a DLL file with the same name from an incorrect directory

• When a Windows application starts, it searches for all the necessary DLL files—small code libraries that assist in making it run efficiently. The DLLs can include functions involving graphics, printing, or file access.
• When the original DLL is absent or not present in the default location, the program starts searching in alternative locations, such as the application's directory, the System32 directory, or even the user's Desktop.
• This is where the actual hijacking occurs. The attacker copies a malicious DLL with the same name to a directory where the application will later search. It's trusted by the system, loaded, and now the malicious code runs—often without triggering any antivirus detection.
• Once the spoofed DLL is loaded, it runs with the same privileges as the application. If the application is running under admin privileges, so is the malware. This can lead to data stealing, system takeover, or complete remote access.
• Due to the fact that DLL Hijacking takes advantage of the fundamental mechanics of Windows DLL loading, it evades many classic antivirus scans. It’s also extremely stealthy—users often have no idea anything went wrong.

Privilege Escalation via DLL Hijacking

One of the worst consequences of DLL hijacking is privilege escalation. Privilege escalation refers to when the attacker acquires greater access than they're intended to—such as a guest user surreptitiously becoming the admin. Some of the Impacts of this

• If an at-risk application is executed with administrator-level privileges, any malicious DLL it loads will also be executed with higher-level privileges. This provides the attacker with control of system-level options, files, or registry entries.
• Bypass Security Mechanisms in which malware can bypass antivirus, UAC (User Account Control), and endpoint security tools if it runs at the same trust level as a whitelisted application. It blends in, becoming more difficult to detect.\
• Persistent System Access in which attackers can change system files, add rootkits, or add new user accounts—giving them long-term unauthorized access, even after a reboot.
• Steal Sensitive Information from this elevated privileges, attackers are able to exfiltrate anything from stored credentials, config files, network secrets, and encrypted vaults. This results in data breaches and information leaks that are difficult to track.
• Hijack Enterprise Systems within corporate settings, DLL hijacking can infect high-trust applications (such as VPN clients or backup applications). This enables attackers to pivot within networks, access Active Directory, or laterally propagate malware across machines.

DLL Hijacking Prevention

DLL Hijacking attacks can be prevented by taking care of the following preventive measures:

• Using third party advance tools: Special advanced tools are designed to prevent cyber attackers to inject harmful code to the system through DLL.
• Update Anti-virus regularly: Having a good quality antivirus and updating the antivirus regularly can help in preventing the hijackers from entering into the computer network system.
• Scan for harmful system vulnerabilities: Regularly monitoring the system vulnerabilities and having a strong defense mechanism can help in preventing vulnerabilities from falling a prey to cyber attackers.
• Enabling MFA Technique: Enabling of Multi-Factor Authentication (MFA) techniques better the security experience and help in reduction of DLL attacks by strengthening the security of the computer networking system.
• Phishing mails should be taken seriously: It is extremely dangerous to open phishing mails that can contribute to Dynamic Load Libraries (DLL) attack. Users must be very careful and should not be opening mails from unknown/ unauthorized senders.

Conclusion

While most attacks alert via sensational ransomware pop-ups, DLL Hijacking is dangerous because it makes no noise. It runs stealthily in the background, fooling Windows programs into loading false code—and before you know it, it's already too late.

From phishing and missing file exploits to privilege escalation and remote backdoors, DLL Hijacking is used by malware authors, APT actors, and cybercrooks to take over everything from home computers to enterprise networks. And because of poor folder permissions and old software, even modern systems are not secure.