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Introduction:
DLL Sideloading—classified by MITRE ATT&CK as T1574.002—is a sophisticated evasion technique where adversaries trick legitimate, often signed Windows applications into loading malicious Dynamic Link Libraries (DLLs) instead of their intended ones. By abusing the Windows DLL search order, attackers can execute arbitrary code under the guise of a trusted process, bypassing security controls that rely on process reputation alone. This technique has been weaponized across the threat landscape—from APT groups like APT29 deploying WinELOADER via vcruntime140.dll sideloading to ransomware families like Charon using Edge.exe to sideload malicious msedge.dll—making it an essential detection and prevention priority for modern security teams.
Learning Objectives:
- Understand the technical mechanics of the Windows DLL search order and how adversaries exploit it for code execution.
- Master the use of Sysmon, Process Monitor, and PowerShell-based scanners to detect and hunt for DLL sideloading activity.
- Implement practical prevention strategies including application whitelisting, directory hardening, and secure DLL loading APIs.
- Understanding the Windows DLL Search Order: The Foundation of the Attack
At the heart of DLL sideloading lies the Windows DLL search order—a predictable sequence Windows follows when an application calls `LoadLibrary()` without specifying a full path. When an application requests a DLL, Windows searches in the following priority order:
- Application Directory – Where the `.exe` is located (highest priority)
2. System Directory – `C:\Windows\System32`
3. 16-bit System Directory – `C:\Windows\System`
4. Windows Directory – `C:\Windows`
5. Current Working Directory (CWD)
6. Directories in the PATH Environment Variable
By placing a malicious DLL in a higher-priority directory—most commonly the application directory itself—an attacker ensures their DLL is loaded instead of the legitimate one located further down the search order. This technique differs from traditional DLL hijacking in that the attacker places both the malicious DLL and the legitimate one together, with the malicious DLL executing attacker-controlled code (e.g., shellcode) and then forwarding all legitimate function calls to the renamed original DLL—a technique known as function proxying. This dual-DLL approach ensures the application runs as expected, effectively masking the malicious activity.
2. Identifying Vulnerable Applications with Process Monitor
To find applications susceptible to DLL sideloading, security professionals and penetration testers leverage Process Monitor (Procmon) from Microsoft Sysinternals.
Step‑by‑step guide to identifying vulnerable applications:
- Launch Process Monitor and clear the existing events.
- Apply the following filters to focus on DLL loading events:
– Process Name → Set to the target application (e.g., OneDriveStandaloneUpdater.exe)
– 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 but cannot find it in the expected location
3. Analyze the results — these failed load attempts indicate that the application does not specify a full path for the DLL, making it vulnerable to sideloading. Common candidates include applications like `Autoruns64.exe` attempting to load `version.dll` from their own directory.
4. Export the original DLL using a tool like CFF Explorer to analyze its exported methods, which you’ll need to proxy in your malicious DLL.
Alternative automated approach — Use lightweight PowerShell-based scanners like DLLHound or dllhound, designed to identify missing or unresolved DLLs and detect potential DLL sideloading vulnerabilities across your Windows environment.
3. Detection and Threat Hunting with Sysmon
Effective detection of DLL sideloading requires visibility into DLL load events. Sysmon EventCode 7 (Image loaded) provides the telemetry necessary to identify suspicious DLL loading patterns.
Sysmon-based detection queries:
Detection 1: DLL Search Order Hijacking Hunt
`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
This query identifies known Windows libraries loaded from non-standard directories—a strong indicator of sideloading activity.
Detection 2: Unsigned Microsoft DLL Side-Loading
`sysmon` EventCode=7
Company="Microsoft Corporation"
Signed=false
SignatureStatus!= Valid
NOT (Image IN ("C:\Program Files (x86)\", "C:\Program Files\", "C:\Windows\System32\", "C:\Windows\SysWow64\"))
NOT (ImageLoaded IN ("C:\Program Files (x86)\", "C:\Program Files\", "C:\Windows\System32\", "C:\Windows\SysWow64\"))
| rex field=Image "(?<ImageFolderPath>.+\\)"
| rex field=ImageLoaded "(?<ImageLoadedFolderPath>.+\\)"
| where ImageFolderPath = ImageLoadedFolderPath
This analytic detects unsigned DLLs masquerading as Microsoft-signed libraries—a technique observed in DarkGate malware campaigns.
Detection 3: PowerShell Core DLL Loaded by Non-PowerShell Process — Detects loading of essential PowerShell DLLs by processes other than powershell.exe, indicating potential PowerShell execution via DLL sideloading (e.g., PowerShdll technique).
4. Prevention and Mitigation Strategies
Preventing DLL sideloading requires a defense-in-depth approach combining system hardening, application control, and secure coding practices.
4.1 Application Whitelisting with Windows Defender Application Control (WDAC)
WDAC (formerly known as Windows Defender Application Control) is one of the most effective measures for mitigating executable file-based malware, including DLL-based attacks. When configured in enforced mode, only code that matches the organization’s allow rules can run; everything else is blocked. However, security teams should note that WDAC can be bypassed via DLL sideloading if DLL signing is not strictly enforced.
4.2 Secure DLL Loading APIs
Developers should use Windows APIs to control the DLL search path:
– `SetDllDirectory` – Allows a process to override the typical search order for DLLs
– `AddDllDirectory` – Adds a directory to the process-specific DLL search path
– `SetDefaultDllDirectories` – Restricts DLL loading to specified directories
Implementation example — Call `SetDllDirectory(“”)` as the first action in `main()` or `WinMain()` to remove the current working directory from the search order, effectively preventing sideloading from the CWD.
4.3 Directory Permission Hardening
Restrict write access to folders where applications are stored, ensuring that only trusted administrators can place DLLs in application directories. Limit user permissions so malware cannot easily exploit DLL sideloading—configure user accounts as Standard Users rather than Administrators.
4.4 Keep Windows Updated
Microsoft regularly patches vulnerabilities exploited in DLL sideloading attacks. Regularly apply Windows updates to benefit from these security improvements.
5. Real-World Attack Scenarios: From APTs to Ransomware
DLL sideloading is not a theoretical threat—it has been weaponized in some of the most sophisticated cyberattacks in recent history.
Charon Ransomware (2025) — Trend Micro researchers uncovered a ransomware campaign targeting the Middle East’s public sector and aviation industry. The attack chain leveraged a legitimate browser-related file, `Edge.exe` (originally named cookie_exporter.exe), to sideload a malicious `msedge.dll` (codenamed “SWORDLDR”), which subsequently decrypted and injected the ransomware payload into `svchost.exe` to evade detection. The ransomware used Curve25519 + ChaCha20 encryption, disabled security tools via a BYOVD (Bring Your Own Vulnerable Driver) attack, and spread via network shares.
APT29 (Cozy Bear) — WinELOADER — The Russian state-sponsored APT group has been documented leveraging WinELOADER to sideload `vcruntime140.dll` for executing malicious code against European diplomatic targets. The campaign used wine-tasting event lures to deliver the GRAPELOADER malware via DLL sideloading.
DarkGate Malware — This Malware-as-a-Service operation has extensively used DLL sideloading, including loading a fake version of `dbgeng.dll` via Cobalt Strike Beacon’s default shellcode stub. Detections focus on monitoring DLL loading, verifying signatures, and flagging unsigned DLLs loaded from suspicious locations.
Salt Typhoon — This threat actor employed DLL sideloading via legitimate antivirus software to deliver the SNAPPYBEE backdoor (also known as Deed RAT), evading traditional security controls.
Stuxnet — The infamous worm used DLL sideloading to distort industrial control system operations at Iran’s Natanz Nuclear Facility, demonstrating that this technique has been a staple of cyber-espionage for over a decade.
6. Advanced Techniques: Function Proxying and ShellcodePack
Modern adversaries and red teams use function proxying to maintain full application compatibility while executing malicious code. The malicious DLL exports all functions of the legitimate DLL and forwards calls to the renamed original DLL rather than reimplementing them.
ShellcodePack automation — Tools like ShellcodePack automate the entire process of generating proxy DLLs and deploying custom payloads. A typical command to generate a proxy DLL:
shellcode_pack.exe -i "C:\msgbox.bin" -G version.dll --dll-proxy="C:\Windows\System32\version.dll" --arch=WIN_X64 --bypass-profile=resources\bypass_profiles\edr_bypass_profile.json
Manual function proxying steps:
- Identify the target application and the DLL it loads (using Procmon)
- Analyze the original DLL using CFF Explorer to find exported methods
- Create a malicious DLL that exports the same functions but forwards calls to the renamed legitimate DLL
7. Forensic Artifacts: ShimCache and Amcache
For incident responders investigating potential DLL sideloading incidents, Windows forensic artifacts provide critical evidence:
- ShimCache (Application Compatibility Cache) — Caches metadata about executed portable executables (PEs), providing valuable information about applications that were executed on the system. It is a live cache kept in system memory and saved to the Windows registry on system shutdown.
-
Amcache — Introduced in Windows 8, Amcache provides a wealth of information about executables and DLLs that interact with the system, recording key metadata that helps investigators piece together a forensic timeline of program activity. Unlike ShimCache, Amcache offers more detailed information about DLL interactions.
Investigators should analyze these artifacts alongside Sysmon logs, Windows Event Logs (especially Audit Process Creation), and file system timestamps to build a comprehensive timeline of DLL sideloading activity.
What Undercode Say:
- DLL sideloading remains one of the most effective adversary techniques because it exploits a fundamental Windows design decision—the search order—rather than a vulnerability that can be simply patched. This makes it a persistent threat requiring continuous monitoring and proactive defense.
-
The convergence of APT-style DLL sideloading with ransomware operations (as seen with Charon) signals a dangerous trend where sophisticated nation-state techniques are being adopted by cybercriminal groups, increasing the risk profile for organizations across all sectors.
-
Effective defense requires a multi-layered approach: application whitelisting (WDAC), secure coding practices (SetDllDirectory), endpoint visibility (Sysmon), and proactive threat hunting. No single control is sufficient against this technique.
-
The availability of automated tools like ShellcodePack and the proliferation of public proof-of-concept code (GitHub hosts numerous DLL sideloading demos) means the barrier to entry for attackers continues to decrease. Organizations must assume DLL sideloading will be attempted and build detection capabilities accordingly.
-
Threat hunting teams should prioritize monitoring for unsigned DLLs loaded from non-standard directories, especially those masquerading as Microsoft-signed libraries. The Splunk Research detections provide an excellent starting point for building custom detection rules.
-
Incident response playbooks must include procedures for analyzing ShimCache and Amcache artifacts to identify executed binaries and loaded DLLs, enabling investigators to reconstruct the attack timeline even after the malicious DLL has been removed.
Prediction:
+1 The continued integration of AI into EDR and XDR platforms will significantly improve automated detection of DLL sideloading patterns, enabling real-time identification of anomalous DLL loading behaviors without relying solely on static signature-based detection.
-1 As Microsoft continues to enhance WDAC and other application control mechanisms, adversaries will increasingly pivot to exploiting custom exclusion rules and misconfigurations in WDAC policies, particularly in complex enterprise environments with VDI or RDP access.
+1 The growing adoption of memory-safe languages and secure-by-design development practices in the software industry may gradually reduce the number of vulnerable applications that fail to specify full DLL paths, shrinking the attack surface over the long term.
-1 Ransomware operators will continue to adopt DLL sideloading as a standard evasion technique, combining it with BYOVD attacks and process injection to disable security tools before encryption—as demonstrated by Charon—making ransomware incidents increasingly difficult to detect and contain.
+1 Threat intelligence sharing and the proliferation of open-source Sigma rules for DLL sideloading detection will enable smaller security teams to implement effective detection strategies without requiring extensive custom research and development.
-1 APT groups will continue to refine DLL sideloading techniques with increasingly sophisticated function proxying and anti-forensic measures, making detection and attribution more challenging for defenders.
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Reported By: 0xfrost Dllsideloading – Hackers Feeds
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