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Introduction:
DLL sideloading is a stealthy exploitation technique that abuses the way Windows searches for and loads Dynamic-Link Libraries (DLLs), allowing attackers to execute malicious code under the guise of a legitimate, signed application. By placing a malicious DLL with the same name and export structure as a legitimate DLL in a location the application checks first, the trusted binary unknowingly loads and executes the attacker’s payload. This technique, mapped to MITRE ATT&CK T1574.002, has been increasingly adopted by threat actors ranging from ransomware groups to advanced persistent threats (APTs) to evade detection and maintain persistence.
Learning Objectives:
- Understand the core mechanics of DLL sideloading and how it differs from DLL hijacking
- Identify real-world attack scenarios and the trusted binaries commonly abused
- Master detection strategies using Sysmon, PowerShell, and Windows Event Logging
- Implement prevention and mitigation techniques including application whitelisting and search path controls
- Apply hands-on commands and configurations to harden Windows environments
You Should Know:
- Understanding the DLL Search Order and Sideloading Mechanics
At the heart of DLL sideloading lies the Windows DLL search order. When an application calls a DLL without specifying a full path, Windows follows a specific sequence to locate it. The search order typically begins with the directory from which the application was loaded, followed by the system directories (C:\Windows\System32), the Windows directory, and finally the directories listed in the PATH environment variable.
Attackers exploit this by placing a malicious DLL in the application’s directory. Since this location is searched first, the application loads the rogue DLL instead of the legitimate one from System32. The malicious DLL must export the same functions as the legitimate one—a technique known as DLL proxying—to ensure the application continues to function normally while the malicious code executes in the background.
A classic real-world example involves the legitimate `msra.exe` (Microsoft Remote Assistance) binary. By simply copying the executable and a malicious DLL into a new folder and launching msra.exe, an attacker can achieve sideloading. Similarly, the `DingTalk.exe` and `ahost.exe` (GitKraken) binaries have been weaponized in recent campaigns to sideload malware.
2. Real-World Attack Scenarios and Impact
DLL sideloading is not a theoretical risk—it is actively exploited in the wild across diverse threat landscapes. In one campaign observed by ReliaQuest, attackers used sideloaded DLLs to drop a Python interpreter onto compromised systems and create a Windows Registry Run key, ensuring the interpreter executed automatically upon each login. This enabled persistent remote access and data theft.
The Lazarus Group, a notorious APT, has leveraged DLL sideloading in Operation DreamJob, targeting European drone firms with the ScoringMathTea RAT. Ransomware operators have also embraced the technique: the Charon ransomware deployed DLL sideloading to deliver its payload, beginning with the execution of a legitimate `Edge.exe` binary that sideloaded a malicious `msedge.dll` (also known as SWORDLDR).
Even commodity malware families like XWorm and DCRat have been observed using DLL sideloading, often via trusted, signed utilities to bypass security defenses. The technique’s appeal lies in its ability to blend malicious activity with legitimate processes, making it difficult for traditional signature-based detection to flag.
- Detection Strategies: Sysmon, Windows Event Logging, and PowerShell
Effective detection of DLL sideloading requires visibility into DLL load events. Sysmon (System Monitor) is the gold standard for this purpose. Specifically, Sysmon Event ID 7 (Image Loaded) logs every DLL loaded by a process, providing the necessary telemetry to identify suspicious activity.
To detect potential sideloading, security analysts should look for Sysmon Event ID 7 events where both the `Image` (the executable) and `ImageLoaded` (the DLL) paths do not match system directories like System32, SysWOW64, or Program Files. This heuristic flags DLLs loaded from non-standard locations—a common indicator of sideloading.
PowerShell-based scanners like DLLHound (also known as dllhound) provide a lightweight approach to identifying missing or unresolved DLLs across running processes. This tool scans all running processes and their loaded libraries, helping defenders pinpoint potential sideloading vulnerabilities on their systems.
Enable Sysmon ImageLoad Events:
To enable Sysmon Event ID 7 logging, add the following to your Sysmon configuration file:
<Sysmon schemaversion="4.81"> <EventFiltering> <RuleGroup name="" groupRelation="or"> <ImageLoad onmatch="include"> <!-- Log all DLL load events --> </ImageLoad> </RuleGroup> </EventFiltering> </Sysmon>
Then apply the configuration:
Sysmon.exe -c config.xml
Detect Suspicious DLL Loads with PowerShell:
The following PowerShell script queries the Security Event Log for suspicious DLL load events (requires enabled logging):
Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-Sysmon/Operational'; ID=7} |
Where-Object { $_.Message -match "ImageLoaded.\(?!System32|SysWOW64|Program Files)" } |
Select-Object TimeCreated, Message
For a more proactive approach, use DLLHound:
Clone and run DLLHound git clone https://github.com/ajm4n/DLLHound.git cd DLLHound .\DLLHound.ps1 -ScanAll
4. Prevention and Mitigation: Hardening Windows Against Sideloading
Preventing DLL sideloading requires a defense-in-depth approach. The most effective measures include:
Application Whitelisting: Deploy AppLocker or Windows Defender Application Control (WDAC) to create policies that control which DLLs and executables can run. This prevents untrusted DLLs from being loaded, even if they reside in the application directory.
Controlling the DLL Search Path: Use the Windows API functions `SetDllDirectory` and `AddDllDirectory` to restrict the DLL search path for your applications. For system-wide control, enable SafeDLLSearchMode via the registry:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager] "SafeDLLSearchMode"=dword:00000001
Code Signing and Path Restrictions: Require code signing for all loaded DLLs and avoid using relative paths for resources. Ensure that applications are configured to load DLLs from trusted, absolute paths.
Vulnerability Identification: Use tools like Windows Feature Hunter (WFH) to identify executable files with potential DLL sideloading vulnerabilities. DLLSpy can help identify sideloading in running processes or static executables.
- Hands-On: Simulating a DLL Sideloading Attack for Defensive Testing
Understanding the attacker’s perspective is crucial for effective defense. The following step-by-step guide demonstrates a basic DLL sideloading simulation for educational and defensive testing purposes.
Step 1: Identify a Vulnerable Application
Use Process Monitor (ProcMon) from Sysinternals to identify applications that attempt to load missing DLLs. Filter by “Path” ending with `.dll` and “Result” set to “NAME NOT FOUND”. This reveals DLLs the application expects but cannot find.
Step 2: Create a Malicious Proxy DLL
Using the DLL proxying technique, create a DLL that exports all functions of the legitimate target DLL and forwards calls to it, while injecting malicious code during `DllMain` or via exported functions. Tools like ShellcodePack can automate this process.
Step 3: Place the Malicious DLL
Copy the legitimate executable and your malicious DLL into a new folder. The DLL must be named exactly as the missing DLL identified in Step 1.
Step 4: Execute and Observe
Launch the executable from the new folder. The application will load your malicious DLL, executing your payload while maintaining normal functionality.
Detection After Simulation:
- Check Sysmon Event ID 7 for the DLL load from the non-system path
- Review Windows Event Logs for anomalous process creation
- Use DLLHound to scan for unresolved dependencies
6. Advanced Evasion and Future Trends
Attackers are continuously refining DLL sideloading techniques to bypass security controls. Recent trends include:
Activation Context Hijacking: Tools like PhantomCtx automate Activation Context hijacking, loading arbitrary DLLs into signed executables without requiring a traditionally vulnerable binary.
Python-Based Payloads: Attackers are increasingly using Python interpreters delivered via sideloading to execute cross-platform payloads, complicating detection.
AI-Powered Detection: Defenders are fighting back with machine learning. Kaspersky’s AI Technology Research Center has trained ML models to detect DLL hijacking based on indirect information about libraries and calling processes. Check Point’s DeepDLL represents another approach to detecting malicious DLLs using deep learning.
Cloud and Container Implications: While traditionally a Windows technique, DLL sideloading concepts are emerging in cloud-1ative environments where dynamic library loading in containers and serverless functions presents similar risks.
What Undercode Say:
- DLL sideloading is a living-off-the-land technique that exploits Windows’ trusted binary ecosystem, making it exceptionally difficult for traditional antivirus to detect.
- Defense requires visibility. Without Sysmon or equivalent logging, sideloading attacks operate in the blind spot of most security operations centers.
- Application whitelisting is the single most effective mitigation. WDAC and AppLocker, when properly configured, can block untrusted DLLs regardless of search order manipulation.
- The attack surface is expanding. As more applications bundle dependencies, the number of potential sideloading vectors continues to grow.
- AI and ML are promising but not silver bullets. While machine learning enhances detection, attackers are already adapting with evasion techniques like control-flow flattening and runtime API reconstruction.
- Proactive hunting beats reactive detection. Regularly scanning for missing DLLs and monitoring unusual load paths should be part of every security team’s routine.
- The human element remains critical. Social engineering campaigns using LinkedIn messages to deliver sideloaded RATs highlight that technical controls must be paired with user awareness training.
- Cloud environments are next. As Windows workloads migrate to the cloud, DLL sideloading will become a cloud security concern, requiring adaptation of detection and response strategies.
- Collaboration and knowledge sharing are key. Webinars and community resources like those from Lancer Infosec play a vital role in equipping defenders with the skills to combat these threats.
Prediction:
- +1 Expect increased adoption of AI-driven detection models for DLL sideloading, with SIEM platforms integrating ML-based anomaly detection as a standard feature within the next 12–18 months.
- -1 The continued proliferation of signed but vulnerable binaries will expand the attack surface, with threat actors maintaining an edge as they discover and weaponize new legitimate applications.
- -1 Ransomware groups will increasingly adopt DLL sideloading as an initial access and defense evasion technique, making it a staple of the cybercriminal toolkit alongside phishing and vulnerability exploitation.
- +1 Microsoft and other vendors will likely introduce additional built-in protections, similar to the SafeDLLSearchMode enhancements in Windows 11 24H2, reducing the effectiveness of basic sideloading attacks.
- -1 The technique will cross platform boundaries, with Linux and macOS implementations of dynamic library loading becoming targets for similar abuse, requiring cross-platform detection capabilities.
- +1 Community-driven tools like DLLHound and Sigma rules will continue to evolve, empowering defenders with free, accessible detection capabilities that level the playing field against well-funded adversaries.
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