Defending Against DLL Hijacking Attacks

With the rise of AI, cybersecurity is moving much more quickly: What felt cutting-edge five years ago is often table stakes today. Yet some attack techniques refuse to fade away. Living-off-the-land (LotL) tactics—where adversaries piggyback on legitimate, signed system tools—have been a headache for defenders for more than a decade. A quieter cousin called living-off-the-library (LotLib) applies the same philosophy to Dynamic Link Libraries (DLLs).

Instead of dropping obviously malicious binaries, a threat actor sidesteps traditional defenses by coercing Windows into loading weaponized or rogue DLLs that masquerade as something the operating system already trusts. This article revisits DLL abuse with fresh eyes, explains why it still lands real-world compromises, and offers practical ideas for strengthening your defenses.

What Exactly Is DLL Hijacking?

Every time you launch a Windows application, that program depends on countless DLLs for added functions—from drawing menus to encrypting traffic. Windows resolves those dependencies by walking through a predetermined search order: current directory first, then system folders, finally environment-specific paths. Attackers exploit this predictable process in several ways:

• DLL preloading or hijacking: A malicious library with the same name as a trusted DLL is placed earlier in the search order, tricking the application into loading the attacker’s code.
  
  

• DLL search order planting: Directories writable by low-privilege users are seeded with weaponized libraries, enabling privilege escalation when a high-privilege service loads them.
  
  

• Side-loading: A legitimate signed executable (often from a reputable vendor) is bundled with a rogue DLL that ships under the guise of a support file. Because the EXE is signed, defenders may glance past the unknown companion library.
  
  

• Reflective loading: An attacker injects a DLL directly into memory without ever touching disk, blurring forensic visibility.

The common theme is stealth: Windows sees a valid file with the right extension in the right place and happily maps it into memory, granting the adversary code-execution inside a signed process.

Why DLL Abuse Still Thrives in 2025

Many security programs improved their behavioral analytics, yet DLL hijacking endures. Three realities keep it alive:

Legacy Software

Enterprises rely on decade-old line-of-business apps that were never patched to load DLLs safely. When vendors disappear or upgrades are expensive, defenders inherit a perpetual vulnerability.

Operational Convenience

Users and administrators often possess write access to application directories for updates or plug-ins. That same convenience grants attackers the foothold needed to plant malicious libraries.

Detection Gaps

EDR solutions typically flag unsigned or unusual executables. But a DLL with a forged certificate or one that piggybacks on a signed process often slips through heuristics. Even if telemetry catches it, the signal drowns in noise because benign DLL loads numbers in the millions on a mid-sized network each day.

Anatomy of a Modern Campaign

Picture a financially motivated group breaching an RDP server with stolen credentials. They pivot laterally, hunting for high-value workstations that run finance software from 2014. After confirming the install path is writable by authenticated users, they craft a malicious version of “libeay32.dll,” a file the app expects for SSL functions.

• Step one: Drop the rogue DLL plus a lightweight launcher that restarts the program to force a fresh load.

• Step two: When the application restarts, Windows naturally discovers the attacker’s DLL in the same directory before consulting the system path.

• Step three: Inside the DLL’s DllMain routine, code spawns a memory-only Cobalt Strike beacon under the protection of the signed vendor executable. Now every outbound connection appears to originate from a trusted process name sitting in “Program Files.”

No noisy PowerShell, no suspicious child processes. Defenders watching for cmd.exe /c whoami miss it entirely. From there, the actor escalates privileges, dumps LSASS via a proc-memory function exported by the rogue DLL, and exfiltrates payroll data after hours.

Red-Team Tricks That Keep Blue Teams Guessing

Modern adversaries refine classic DLL abuse with extra flourishes:

• Function forwarding: They copy exported function names from the original DLL and forward legitimate calls to the genuine library loaded under a different name. The application runs normally, hiding malicious behavior.
  
  

• Time-stomped compile dates: Build times are back-dated to align with vendor release cycles, avoiding oddball timestamps that might raise red flags.
  
  

• Domain fronting in the payload: The DLL’s C2 beacons blend into Microsoft or Google cloud traffic, making network-based detection harder.
  
  

• In-memory patching of ETW: The DLL disables Event Tracing for Windows on the fly, cutting off telemetry at the source.

Knowing these tricks helps defenders appreciate why purely reactive measures often fall short.

Blue-Team Countermeasures That Actually Work

While you can’t rewrite decades of software overnight, layered mitigations force attackers to burn more time and custom tooling. Prioritize the following:

• Audit application directories: Regularly scan for writable folders under “Program Files” or service paths that run as SYSTEM. Revoke write permissions wherever feasible.
  
  

• Implement DLL signing enforcement: Windows 10+ provides WDAC policies that block unsigned or unapproved libraries from loading into protected processes. Pilot the ruleset on non-production systems, then graduate to wider enforcement.
  
  

• Catalog legitimate hashes: Build an allow-list of expected DLL checksums for business-critical apps. EDR platforms like SentinelOne and CrowdStrike support hash integrity rules that alert on drift.
  
  

• Monitor anomalous load paths: Create detections for high-privilege services loading DLLs from user profiles, temp folders, or network shares—locations seldom used by developers.
  
  

• Embrace Sysmon and ETW: Configure Sysmon Event ID 7 (Image Load) alongside ETW’s Microsoft-Windows-Sysmon/Operational channel to capture metadata every time a DLL enters memory. Funnel logs into a SIEM, then applies frequency-based analytics instead of raw signature checks.
  
  

• Patch search order flaws: Where source code is available, add explicit calls to SetDllDirectory or LoadLibraryEx with the LOAD_LIBRARY_SEARCH_FLAG options to bypass the classic search order entirely.
  
  

Stacked together, these steps don’t guarantee immunity, but they raise the bar high enough that most profit-focused actors move on to softer targets.

Closing Thoughts

DLL hijacking has been documented since at least Windows XP, yet the technique remains a staple in breach reports and red-team after-action reviews. The reason is simple: it leverages built-in OS behavior instead of novelty, making it devilishly reliable and deceptively quiet. For organizations invested in serious Cybersecurity & Cyberdefense, ignoring living-off-the-library attacks is no longer an option.

Start by identifying exposed directories, enforce trusted signing where practical, and collect detailed image-load telemetry. With visibility in place and permission hygiene dialed in, the next time an attacker tries to slip a rogue DLL into your environment, they’ll trip a dozen alarms long before they reach your crown-jewel data.