name: detecting-dll-sideloading-attacks description: Detect DLL side-loading attacks where adversaries place malicious DLLs alongside legitimate applications to hijack execution flow for defense evasion. domain: cybersecurity subdomain: threat-hunting tags:

• threat-hunting
• mitre-attack
• dll-sideloading
• defense-evasion
• t1574
• edr
• proactive-detection

version: '1.0' author: mahipal license: Apache-2.0 d3fend_techniques:

• File Metadata Consistency Validation
• Content Format Conversion
• File Content Analysis
• Platform Hardening
• File Format Verification

nist_csf:

• DE.CM-01
• DE.AE-02
• DE.AE-07
• ID.RA-05

mitre_attack:

• T1046
• T1057
• T1082
• T1083
• T1027

Detecting DLL Sideloading Attacks

When to Use

• When investigating potential DLL hijacking in enterprise environments
• After EDR alerts on unsigned DLLs loaded by signed applications
• When hunting for APT persistence using legitimate application wrappers
• During incident response to identify trojanized applications
• When threat intel indicates DLL sideloading campaigns targeting specific software

Prerequisites

• EDR with DLL load monitoring (CrowdStrike, MDE, SentinelOne)
• Sysmon Event ID 7 (Image Loaded) with hash verification
• Application whitelisting or DLL integrity monitoring
• Software inventory of legitimate applications and expected DLL paths
• Code signing verification capabilities

Workflow

1. Identify Sideloading Targets: Research known vulnerable applications that load DLLs without full path qualification (LOLBAS, DLL-sideload databases).
2. Monitor DLL Load Events: Query Sysmon Event ID 7 for DLL loads where the DLL path differs from the application's expected directory.
3. Check DLL Signatures: Flag unsigned or untrusted DLLs loaded by signed executables.
4. Detect Path Anomalies: Identify legitimate executables running from unusual locations (Temp, AppData, Public) that may be decoy wrappers.
5. Hash Verification: Compare loaded DLL hashes against known-good versions and threat intel feeds.
6. Correlate with Process Behavior: Check if the host process exhibits unusual behavior (network connections, child processes) after loading the suspicious DLL.
7. Document and Remediate: Report sideloading instances, quarantine malicious DLLs, and update detection rules.

Key Concepts

Tools & Systems

Common Scenarios

1. Legitimate App Wrapper: Adversary copies signed application (e.g., OneDrive updater) to temp folder alongside malicious DLL with same name as expected dependency.
2. Phantom DLL Exploitation: Malicious DLL placed in PATH location where legitimate app searches for non-existent DLL.
3. DLL Proxy Loading: Malicious version.dll proxies all exports to real version.dll while executing malicious code on DllMain.
4. Software Update Hijack: Attacker replaces DLL in update staging directory before legitimate updater loads it.

Output Format

Hunt ID: TH-SIDELOAD-[DATE]-[SEQ]
Technique: T1574.002
Host Application: [Legitimate signed executable]
Sideloaded DLL: [Malicious DLL name and path]
Expected DLL Path: [Where DLL should legitimately be]
DLL Signed: [Yes/No]
App Location: [Expected/Anomalous]
Host: [Hostname]
Risk Level: [Critical/High/Medium/Low]