Learn what DLL hijacking is, why it’s dangerous, and how to protect Windows apps from this stealthy attack, with practical tips and real-world examples.
DLL side loading is when attackers trick an application into loading a malicious Dynamic Link Library (DLL) instead of the legitimate one. Essentially, it’s a sneaky way to bypass security measures and run harmful code.
Key Takeaways
- DLL side loading tricks legitimate applications into running malicious code. Cybercriminals exploit the way some programs search for DLL files by planting a fake, malicious file with the same name as the trusted one. When the application loads the wrong DLL, the attacker's code runs instead of the original, giving them access to your system.
- It is a particularly stealthy and persistent attack method. Trusted software is seen by users and sometimes security tools as safe, so loading a malicious DLL through these programs can go unnoticed and remain persistent for a long time. Attackers commonly use this technique to spread malware, create backdoors, or exfiltrate sensitive data.
- Older and misconfigured environments remain most at risk. Modern operating systems and well-designed applications have tightened their DLL loading mechanisms, but vulnerabilities still exist, especially in older software or environments without updated security protocols.
- Defense requires a layered, proactive approach. Key protective measures include keeping software updated, limiting user permissions, monitoring file locations with endpoint protection tools, and deploying advanced detection systems to spot unusual DLL-loading behavior before it escalates into a larger incident.
Breaking it down: DLL Side Loading explained
DLLs are files used by programs to execute certain functions, like connecting to the internet or reading files. Normally, applications look for these DLL files in specific locations—but here’s where things get tricky.
Cybercriminals exploit the way some programs search for DLLs by planting a fake, malicious file with the same name as the trusted one. When the application loads the wrong DLL, the attacker’s code runs instead of the original, giving them access to your system.
Why DLL Side Loading matters in cybersecurity
DLL side loading poses a significant risk because it allows attackers to piggyback on legitimate programs to infiltrate systems. Trusted software is seen by users (and sometimes security tools) as safe, so loading a malicious DLL through these programs can go unnoticed and remain persistent for a long time. Often, attackers use this technique to spread malware, create backdoors, or exfiltrate sensitive data.
Modern operating systems and well-designed applications have tightened their DLL loading mechanisms, but vulnerabilities still exist, especially in older software or environments without updated security protocols.
How to protect your organization:
Keep software updated: Regularly update applications to patch known vulnerabilities that attackers frequently exploit.
Limit user permissions: Avoid running programs as an administrator unless absolutely necessary.
Monitor file locations: Use endpoint protection tools to flag any suspicious files in critical directories.
Educate your team: Empower your team with security awareness training to avoid downloading apps or files from shady sources.
Invest in security: Deploy advanced detection systems to spot unusual DLL-loading behavior before it becomes a full-blown problem.
DLL side loading highlights the importance of staying vigilant and proactive. Securely configuring applications and staying ahead of updates is your best defense against clever tricks like these.
Why attackers love DLL Side-Loading
DLL side-loading is attractive to attackers because it lets malicious code run under the cover of a legitimate, trusted application — making detection and blocking significantly harder. It is mapped to MITRE ATT&CK under Hijack Execution Flow (T1574.002) and consistently appears in both commodity malware campaigns and sophisticated, targeted intrusions.
It abuses trusted, signed binaries. Attackers look for legitimate applications that load DLLs from their current directory or from writable paths without strict validation, then drop a malicious DLL with the expected filename right next to the executable. The trusted program does the heavy lifting for them. Huntress has observed this pattern with a range of legitimate applications, including tools like ADNotificationManager.exe and DLPUserAgent.exe, being co-opted to load malicious payloads without any modification to the binaries themselves.
It is purpose-built for defense evasion. Because the parent process is a well-known, signed application, security tools are far less likely to flag its activity as suspicious. This is exactly why the technique falls under the "defense evasion" tactic in MITRE ATT&CK. The malicious DLL rides inside a trusted process and can inherit that process's implicit "trust" — making it harder for both security appliances and human analysts to catch.
It hides in the noise. Side-loaded DLLs are typically dropped into locations that already contain a high volume of legitimate application files, such as %ProgramData% subdirectories and user profile data folders. Unsigned DLLs sitting in these directories are a well-documented tradecraft marker, but they can be easy to overlook without dedicated monitoring. In the Huntress investigation into a fake tech support campaign delivering Havoc C2, malicious DLLs were dropped into %PROGRAMDATA%\Adobe\ARM — a location designed to blend in with legitimate Adobe software activity.
It enables stealthy, boot-persistent access. Once a vulnerable application is configured to run at startup or is already installed as a service, a malicious DLL placed beside it will be loaded automatically on every boot. In the Havoc C2 campaign observed by Huntress, adversaries went a step further, deploying scheduled tasks that reconstructed and relaunched the side-loaded payload on each system restart — ensuring persistence even after initial remediation attempts.
DLL Side Loading FAQs
DLL side loading exploits trusted programs, making it tricky to detect. Once loaded, malicious DLLs can steal data, plant spyware, or open backdoors for other attacks.
An attacker replaces or plants a fake DLL file in a location your program checks first. When the application runs, it unknowingly loads the attacker’s malicious code instead of the legitimate file.
Look for unexpected behavior in trusted applications, changes in DLL file locations, or alerts from endpoint protection software. Regular system scans can also help.
Yes, although newer systems have better defenses, older software and misconfigured environments are still vulnerable. Attackers often exploit overlooked settings or outdated applications.
Additional Resources
- Read more about What Is DLL Hijacking? How to Detect & Prevent It
- Read more about What is an Exploit Kit?Learn what exploit kits are, how they work, and why they're dangerous. Comprehensive guide covering detection, prevention, and current threats for cybersecurity professionals.
- Read more about What is an Exploit Pack? Definition & Defense GuideLearn how exploit packs work, why they're dangerous, and how to protect your organization from these automated cyberattack tools.
- Read more about What is a Foothold in Cybersecurity?Learn what a foothold is in cybersecurity, how attackers use it to infiltrate organizations, and ways to protect against it.
- Read more about What is Anti-Spyware & How Does It Protect Your Devices?Learn what anti-spyware is, how it works, and its role in cybersecurity. Uncover steps to protect your devices and data effectively.
- Read more about What is TCP/IP and Its Importance in CybersecurityLearn the importance of TCP/IP in cybersecurity with a deep look at its layers, vulnerabilities, defenses, and tools for securing traffic.
- Read more about What is File Integrity Monitoring (FIM)?Protect your files with File Integrity Monitoring (FIM). Learn how it detects unauthorized changes, prevents security breaches, and strengthens your cybersecurity defenses.
- Read more about What is Horizontal Port Scan?Hackers use horizontal port scans to find vulnerabilities across devices on a network. Protect your systems by staying vigilant and fortifying your defenses!
- Read more about What Is Traitorware? How Hackers Weaponize Legit AppsTraitorware turns trusted apps into cyber weapons, bypassing MFA and hiding in plain sight. Learn how these attacks work and what you can do to stay protected.
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