What Is DLL Hijacking? Understanding and Preventing the Threat

DLL hijacking is a long-standing exploitation technique that remains highly useful to hacking groups and Advanced Persistent Threat actors (APTs) in 2025. It allows attackers to execute malicious code by abusing how Windows loads Dynamic Link Library (DLL) files.

Although the method originated as far back as Windows XP, it remains a persistent threat for executing code via DLL in post-exploitation and persistence scenarios—especially in state-backed campaigns.

How DLL Hijacking Works

Understanding how DLL hijacking works requires knowing how Windows searches for and loads DLLs. When an application requests a DLL without specifying its full path, Windows searches directories in a specific order. If an attacker places a malicious DLL file earlier in that path, Windows loads that file instead of the legitimate one.

This lets the attacker run unauthorized code under the same privileges as the original application. Because it exploits native OS behavior, this dynamic link library attack is often invisible to antivirus software.

A typical hijacking chain involves:

• Target identification: Choosing an application with unsafe DLL loading behavior
• Payload creation: Crafting a DLL with code for data exfiltration, lateral movement, or privilege escalation
• DLL placement: Dropping the file in a location prioritized by Windows’ search order
• Execution: Launching the app, which unknowingly loads the attacker’s payload

Real-World DLL Hijacking Examples

Several high-profile malware campaigns have used DLL hijacking as a core delivery method:

• Stuxnet: Used DLL sideloading to distort how industrial control systems operated at Natanz Nuclear Facility in one of the most notorious hacks of the century.
• PlugX: An APT tool widely attributed to Chinese actors targeting manufacturing, insurance, nonprofits, and more.
• Cobalt Strike: Cobalt Strike, a pentesting tool that bad actors also use, is commonly deployed via DLLs.

Despite being well-documented, the technique continues to succeed due to legacy application flaws and weak file path hygiene.

Why DLL Hijacking Persists in 2025

This threat endures because:

• Legacy and in-house apps often use insecure DLL load methods
• Internal tools are rarely audited for dynamic link library attack exposure
• Elevated app permissions increase the risk if DLLs are hijacked
• Vendors may ship software with unsafe load paths, expanding supply chain attack risk

When insecure DLL loading stems from a vendor application, it becomes a supply chain risk. If an attacker exploits that flaw, they can impact downstream customers.

Detecting DLL Hijacking

Detection methods go beyond traditional signature-based antivirus. Effective controls include:

• Monitoring DLL load paths for anomalies
• Flagging unsigned DLLs used by signed apps
• Tracking suspicious executing code via DLL behavior through EDR telemetry
• Simulating DLL injection as part of red/blue team exercises

These practices are essential to uncover threats that hide within normal OS operations.

Prevent DLL Injection and Sideloading

To prevent DLL-based attacks, security teams must focus on development and system-level controls:

• Use fully qualified paths in application code
• Enable SafeDllSearchMode in Windows to prioritize system directories
• Apply access control lists (ACLs) to restrict file writing in app folders
• Digitally sign all DLLs and validate their integrity before use
• Use solutions to designate approved applications, like AppLocker or Windows Defender Application Control (WDAC)
• Avoid placing DLLs in writable or shared directories

DLL hijacking mitigation begins in the software development lifecycle and continues through configuration management and vendor review.

Defense-in-Depth for DLL Hijacking Mitigation

Because DLL hijacking operates at the OS and app level, no single control is sufficient. A defense-in-depth strategy should include:

• Endpoint telemetry to detect DLL sideloading
• Secure coding practices to avoid Windows DLL vulnerability patterns
• Vendor assessments using platforms like SecurityScorecard
• Network segmentation to contain successful hijacks
• Incident response protocols to react quickly when suspicious DLL behavior occurs

These layers make it far more difficult for an attacker to move laterally or escalate privileges after initial access.

Executive Summary

DLL hijacking is an enduring and low-noise method for executing code via DLL, bypassing many security controls by imitating normal behavior. In 2025, as enterprise software stacks and vendor ecosystems grow, this technique remains effective.

Security teams must evaluate how applications load libraries and ensure both internal and vendor software meet safety standards. Preventing DLL injection isn’t just about antivirus—it’s about hardening applications, verifying binaries, keeping up-to-date on threat intelligence, and managing third-party risk. Together, these practices reduce the attack surface and improve resilience against known trick in the threat actor playbook.

SecurityScorecard identifies external risks that may correlate with broader attack vectors like DLL hijacking.

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