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Introduction:
DLL sideloading is one of the most insidious attack vectors in the modern Windows threat landscape. By abusing the legitimate Windows DLL search order, attackers can trick signed, trusted applications into loading malicious code while maintaining full application functionality — allowing them to bypass traditional signature-based defenses and operate stealthily under the guise of legitimate processes. This article explores the fundamentals of DLL sideloading, real-world attack case studies, and actionable detection and prevention strategies to help security professionals stay ahead of adversaries.
Learning Objectives:
- Understand the Windows DLL search order and how attackers exploit it for sideloading attacks
- Learn to identify vulnerable applications using process monitoring and analysis tools
- Master detection techniques using Sysmon, Windows Event Logging, and threat hunting queries
- Implement practical prevention measures including application whitelisting, privilege restriction, and system hardening
- Analyze real-world attack campaigns leveraging DLL sideloading for malware distribution and persistence
- Understanding the Windows DLL Search Order — The Core Vulnerability
DLL sideloading exploits the fundamental way Windows locates and loads Dynamic Link Libraries. When an application calls `LoadLibrary(“example.dll”)` without specifying a full path, Windows searches for the DLL in a specific sequence of directories:
- Application Directory — where the .exe is located (highest priority)
2. System32 (C:\Windows\System32)
3. System Directory (C:\Windows\System)
4. Windows Directory (C:\Windows)
5. Current Working Directory
6. Directories listed in the PATH environment variable
The critical flaw: by placing a malicious DLL in the application directory (the highest priority location), an attacker can intercept the loading process before Windows reaches the legitimate system directory where the real DLL resides. The malicious DLL executes attacker-controlled code and then forwards all legitimate function calls to the renamed original DLL — ensuring the application continues to function normally while the attack proceeds undetected.
Step-by-Step Guide — Identifying Vulnerable Applications:
To find applications susceptible to DLL sideloading, use Process Monitor (Procmon) from Microsoft Sysinternals:
1. Download and launch Process Monitor
- Apply the following filters to isolate DLL loading events:
– Process Name: Set to the target application
– Operation: Filter for `Load Image` to capture DLL loading attempts
– Result: Filter for `NAME NOT FOUND` to identify cases where the application searches for a DLL that doesn’t exist in the expected location
3. Analyze the results — look for DLLs that Windows attempted to load from the application directory but couldn’t find
4. Common vulnerable DLLs include version.dll, winmm.dll, and libcares-2.dll, as many applications attempt to load these from their own directory without specifying a full path
Linux/Windows Commands for DLL Analysis:
Windows - List all DLLs loaded by a specific process Get-Process -1ame "processname" | Select-Object -ExpandProperty Modules Windows - Use Sysinternals Sigcheck to verify DLL signatures sigcheck.exe -a -e C:\Path\To\Suspicious.dll Windows - Check DLL search order for a specific application dumpbin.exe /dependents C:\Path\To\Application.exe Windows - Monitor DLL load events in real-time using Sysmon (Requires Sysmon installed with appropriate configuration)
- Real-World Attack Campaigns — DLL Sideloading in Action
DLL sideloading has been weaponized in numerous high-profile cyberattacks, demonstrating its effectiveness as an initial access and evasion technique.
Case Study 1: LinkedIn Phishing Campaign (2026)
Attackers approached high-value individuals through LinkedIn messages, establishing trust and deceiving them into downloading a malicious WinRAR self-extracting archive. The archive contained:
– A legitimate open-source PDF reader application
– A malicious DLL sideloaded by the PDF reader
– A Python interpreter portable executable
– A decoy RAR file
When the PDF reader launched, it sideloaded the rogue DLL, which dropped the Python interpreter and created a Windows Registry Run key for persistence. The interpreter executed Base64-encoded shellcode directly in memory to avoid forensic artifacts, establishing remote access and data exfiltration capabilities. This campaign exploited the fact that social media platforms are typically less monitored than email, allowing attackers to bypass detection at scale.
Case Study 2: Multi-Actor ahost.exe Campaign
The Trellix Advanced Research Center uncovered an active campaign exploiting a DLL sideloading vulnerability in the legitimate `ahost.exe` utility (part of the c-ares DNS resolver library, commonly bundled with Git for Windows and developer tools like GitKraken).
Attackers paired a malicious `libcares-2.dll` with any signed version of `ahost.exe` (often renamed) to execute their code. The campaign delivered commodity malware including infostealers (AgentTesla, FormBook, Lumma Stealer, Vidar, CryptBot) and Remote Access Trojans (Remcos, QuasarRAT, DCRat, XWorm). Targets were typically employees in finance, procurement, and supply chain roles.
Case Study 3: Charon Ransomware
Trend Micro identified the Charon ransomware strain deployed via DLL sideloading against aviation and public sector entities in the Middle East. The attack used a legitimate `Edge.exe` to load a malicious `msedge.dll` (“SWORDLDR”), which decrypted and injected the ransomware payload into `svchost.exe` to evade detection.
- Detection Strategies — Finding the Needle in the Haystack
Detecting DLL sideloading is challenging because attackers use legitimate, signed applications to execute their code. However, a layered detection approach can identify suspicious activity.
3.1 Sysmon-Based Detection
Sysmon EventCode 7 (Image Loaded) provides detailed visibility into DLL loading events. The following Splunk query identifies potential DLL sideloading by detecting known Windows libraries loaded from non-standard directories:
`sysmon` EventCode=7 NOT (process_path IN ("\system32\", "\syswow64\","\winsxs\","\wbem\"))
| lookup hijacklibs library AS loaded_file OUTPUT islibrary
| search islibrary = True
| stats count min(_time) as firstTime max(_time) as lastTime by Image ImageLoaded dest loaded_file loaded_file_path original_file_name process_exec process_guid process_hash process_id process_name process_path service_dll_signature_exists service_dll_signature_verified signature signature_id user_id vendor_product
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
3.2 Windows Event Logging
Enable Audit Process Creation in Local Security Policy to track DLL loads from unauthorized folders. Monitor for:
– DLLs loaded from temporary directories (%TEMP%, C:\Users\\AppData\Local\Temp)
– Signed executables loading unsigned DLLs from non-standard paths
– Known abused DLLs (version.dll, winmm.dll, libcares-2.dll) loaded from suspicious locations
3.3 Threat Hunting with Process Explorer
Use Process Explorer from Microsoft Sysinternals to investigate running processes:
1. Launch Process Explorer as Administrator
- Click on a process and select “Properties” → “Strings” or use the DLL view
- Look for DLLs loaded from unexpected directories (e.g., application directory instead of System32)
- Verify digital signatures of loaded DLLs — unsigned DLLs loaded by signed applications are a red flag
Windows Commands for Detection:
Windows - List all running processes with their loaded modules
Get-Process | ForEach-Object { $_.Modules } | Select-Object ModuleName, FileName, ProcessName
Windows - Find unsigned DLLs loaded by signed processes
Get-Process | ForEach-Object {
$<em>.Modules | ForEach-Object {
if ((Get-AuthenticodeSignature $</em>.FileName).Status -1e "Valid") {
Write-Output "$($<em>.ProcessName) - $($</em>.FileName)"
}
}
}
Windows - Check for DLL sideloading indicators using Sysmon logs (requires Sysmon)
Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-Sysmon/Operational'; ID=7} |
Where-Object { $_.Message -match "ImageLoaded.\[^\]+\(version|winmm|libcares-2).dll" }
4. Prevention and Mitigation — Hardening Your Defenses
Preventing DLL sideloading requires a multi-layered security approach.
4.1 Enable SafeDllSearchMode
Windows provides the `SafeDllSearchMode` registry setting that changes the DLL search order to prioritize system directories before the current working directory:
Windows - Enable SafeDllSearchMode (requires admin) reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager" /v SafeDllSearchMode /t REG_DWORD /d 1 /f Windows - Verify SafeDllSearchMode is enabled reg query "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager" /v SafeDllSearchMode
4.2 Application Whitelisting
Configure Windows Defender Application Control (WDAC) or AppLocker to only allow approved applications and DLLs. This prevents unauthorized DLLs from being loaded regardless of their location.
4.3 Restrict User Privileges
Limit user permissions to prevent malware from exploiting DLL sideloading:
Windows - Check user privileges whoami /priv Windows - Remove users from local Administrators group net localgroup Administrators "username" /delete
4.4 Keep Software Updated
Microsoft regularly patches vulnerabilities exploited in DLL sideloading attacks:
Windows - Check for and install updates Get-WindowsUpdate -Install -AcceptAll
4.5 Harden Directory Permissions
Restrict write access to folders where applications are stored:
Windows - Restrict write access to Program Files icacls "C:\Program Files" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" "Administrators:(OI)(CI)F" "Users:(OI)(CI)R"
5. Advanced Techniques — Function Proxying and Tooling
For security researchers and red team professionals, understanding the mechanics of DLL sideloading is essential for both attack simulation and defense.
5.1 Function Proxying with ShellcodePack
ShellcodePack automates the process of generating proxy DLLs that maintain full application compatibility. The tool creates a malicious DLL that exports all functions of the legitimate DLL and forwards calls to the original while executing payload shellcode.
Command Example — Generating a Proxy DLL:
Generate shellcode payload (using msfvenom) msfvenom -p windows/exec CMD=calc.exe -f c -b "\x00" -o shellcode.bin Generate proxy DLL using ShellcodePack shellcode_pack.exe -i "C:\shellcode.bin" -o "version.dll" -t "version"
5.2 DLL Proxying Explained
DLL proxying involves creating a malicious DLL that exports all functions of the legitimate DLL and forwards calls to the original. This ensures the application continues to function normally while the malicious code executes.
Tools for DLL Sideloading Research:
- LazyDLLSideload (Rust-based) — Automatically parses PE export tables and generates ready-to-compile proxy DLL projects
- DLLProxyFramework — Generates proxy DLLs for sideloading and hijacking research, mirrors exports, and embeds originals
- Process Monitor (Procmon) — Identifies vulnerable applications by monitoring NAME NOT FOUND DLL load events
6. MITRE ATT&CK Mapping and Threat Intelligence
DLL sideloading is mapped to MITRE ATT&CK under T1574.001 — Hijack Execution Flow: DLL Search Order Hijacking. Key sub-techniques include:
- T1574.001 — DLL Search Order Hijacking
- T1574.002 — DLL Side-Loading (specifically abusing WinSxS)
- T1218 — Signed Binary Proxy Execution (using LOLBins like
rundll32.exe,regsvr32.exe)
Threat actors increasingly combine DLL sideloading with Living Off the Land (LOLBins) to evade detection. Common LOLBins abused in sideloading attacks include:
– `rundll32.exe` — Executes exported functions from DLLs
– `regsvr32.exe` — Registers DLLs and executes DllInstall
– `msra.exe` — Microsoft Remote Assistance (vulnerable to sideloading)
7. What Undercode Say:
- DLL sideloading is not a vulnerability — it’s a design feature. Windows behaves exactly as designed when loading DLLs from the application directory first. The “vulnerability” lies in applications that don’t specify full paths and in environments that lack proper hardening. Security teams must treat this as a configuration and monitoring problem, not just a patching issue.
-
The rise of AI-powered detection is changing the game. Kaspersky’s research shows that machine learning models can now detect DLL hijacking attempts based on indirect information about the library and the process that called it. As attackers increasingly use DLL sideloading to bypass traditional signatures, AI-driven behavioral analysis will become the frontline defense.
-
Supply chain and developer tools are the new attack surface. The ahost.exe campaign demonstrates how open-source libraries and developer tools are becoming prime targets for DLL sideloading attacks. Organizations must extend their security monitoring to include development environments and third-party dependencies, not just production systems.
-
Detection requires proactive hunting, not just alerts. The most effective DLL sideloading detections rely on hunting queries that identify anomalies — such as known Windows libraries loaded from non-standard directories — rather than waiting for signature-based alerts. Security teams must invest in threat hunting capabilities and leverage tools like Sysmon and Splunk to stay ahead.
-
Education and awareness are critical countermeasures. The LinkedIn phishing campaign succeeded because attackers exploited human trust, not just technical vulnerabilities. Organizations must train employees to recognize social engineering tactics, especially on platforms outside traditional email channels.
Prediction:
-
+1 DLL sideloading will remain a top attack vector through 2026-2027 as attackers continue to exploit the inherent trust in signed applications and the complexity of the Windows DLL loading mechanism.
-
+1 AI-powered detection systems will significantly reduce the success rate of commodity DLL sideloading attacks, forcing advanced adversaries to develop more sophisticated evasion techniques.
-
-1 The proliferation of open-source libraries and developer tools will create new sideloading opportunities, as demonstrated by the ahost.exe and c-ares campaigns.
-
-1 Organizations without EDR/XDR solutions and proactive threat hunting capabilities will remain highly vulnerable, as traditional antivirus and signature-based defenses are largely ineffective against DLL sideloading.
-
+1 Microsoft’s continued investment in Windows Defender Application Control and memory integrity features will gradually reduce the attack surface, but legacy applications and misconfigured environments will persist as weak points for years to come.
▶️ Related Video (80% Match):
https://www.youtube.com/watch?v=0gTPSLTwT08
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