What it does. Detect DLL side-loading and search-order hijacking (MITRE T1574) where adversaries plant malicious DLLs for legitimate signed applications to load, by analyzing Sysmon Event ID 7 DLL-load events, checking signatures/hashes against known-good versions, and flagging path anomalies with EDR tools like CrowdStrike, MDE, or SentinelOne. Use when investigating EDR alerts on unsigned DLLs, hunting for APT persistence via trojanized applications, or triaging incidents involving DLL hijacking. Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill detecting-dll-sideloading-attacks, or copy the skill folder into ~/.claude/skills/detecting-dll-sideloading-attacks/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/detecting-dll-sideloading-attacks/SKILL.md

SKILL.md (verbatim)

name: detecting-dll-sideloading-attacks
description: Detect DLL side-loading and search-order hijacking (MITRE T1574) where adversaries plant malicious DLLs for legitimate signed applications to load, by analyzing Sysmon Event ID 7 DLL-load events, checking signatures/hashes against known-good versions, and flagging path anomalies with EDR tools like CrowdStrike, MDE, or SentinelOne. Use when investigating EDR alerts on unsigned DLLs, hunting for APT persistence via trojanized applications, or triaging incidents involving DLL hijacking.
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]

Other files in this skill

• LICENSE
• assets/template.md
• references/api-reference.md
• references/standards.md
• references/workflows.md
• scripts/agent.py
• scripts/process.py

assets/template.md (verbatim)

DLL Sideloading Hunt Template

Hunt Metadata

Hypothesis

[e.g., "Adversaries are using DLL sideloading with legitimate signed applications to execute malicious payloads while evading detection."]

Findings

Recommendations

1. Block: [Quarantine malicious DLLs]
2. Harden: [Application directory permissions, DLL safe search mode]
3. Detect: [Sysmon Event ID 7 rules for known targets]

references/api-reference.md (verbatim)

API Reference: Detecting DLL Sideloading Attacks

Sysmon Event ID 7 (Image Loaded)

<EventID>7</EventID>
<Data Name="Image">C:\Users\victim\app\signed.exe</Data>
<Data Name="ImageLoaded">C:\Users\victim\app\malicious.dll</Data>
<Data Name="Signed">false</Data>
<Data Name="SignatureStatus">Unavailable</Data>
<Data Name="Hashes">SHA256=abc123...</Data>

python-evtx Usage

import Evtx.Evtx as evtx
with evtx.Evtx("Sysmon.evtx") as log:
    for record in log.records():
        xml = record.xml()
        # Filter EventID 7, check Signed=false, non-standard path

Known Sideloading Targets

Splunk SPL Detection

index=sysmon EventCode=7 Signed=false
| where NOT match(ImageLoaded, "(?i)(System32|SysWOW64|Program Files)")
| stats count by Image, ImageLoaded, SignatureStatus, Computer
| where count > 0

Sigma Rule Fields

logsource:
  product: windows
  category: image_load
detection:
  selection:
    EventID: 7
    Signed: "false"
  filter:
    ImageLoaded|startswith:
      - "C:\\Windows\\System32\\"
      - "C:\\Program Files\\"

CLI Usage

python agent.py --sysmon-log Sysmon.evtx
python agent.py --scan-dir C:\Users\victim\Downloads\app\
python agent.py --generate-sigma

references/standards.md (verbatim)

Standards and References - DLL Sideloading Detection

MITRE ATT&CK Mappings

T1574.002 - Hijack Execution Flow: DLL Side-Loading

• Tactic: Persistence (TA0003), Privilege Escalation (TA0004), Defense Evasion (TA0005)
• Platforms: Windows
• Data Sources: File monitoring, DLL monitoring, Process monitoring

Related Techniques

Windows DLL Search Order

1. Directory of the executable (or directory specified by SetDllDirectory)
2. System32 directory
3. 16-bit system directory
4. Windows directory
5. Current working directory
6. PATH environment variable directories

Known Vulnerable Applications

Detection Data Sources

references/workflows.md (verbatim)

Detailed Hunting Workflow - DLL Sideloading

Phase 1: Sysmon DLL Load Analysis

Step 1.1 - Unsigned DLLs Loaded by Signed Applications

index=sysmon EventCode=7 Signed=false
| where match(Image, "(?i)\\\\(Program Files|Windows)\\\\")
| where NOT match(ImageLoaded, "(?i)\\\\(Windows|Program Files)\\\\")
| stats count by Image ImageLoaded Signature Computer
| sort -count

Step 1.2 - DLL Loads from Unusual Directories

index=sysmon EventCode=7
| where match(ImageLoaded, "(?i)(\\\\temp\\\\|\\\\appdata\\\\|\\\\public\\\\|\\\\downloads\\\\)")
| where Signed=false OR Signature="?"
| stats count by Image ImageLoaded Computer User
| sort -count

Step 1.3 - KQL for MDE DLL Sideloading

DeviceImageLoadEvents
| where Timestamp > ago(7d)
| where InitiatingProcessFileName in~ ("OneDriveUpdater.exe","DismHost.exe","WerFault.exe")
| where not(FolderPath startswith "C:\\Windows" or FolderPath startswith "C:\\Program Files")
| project Timestamp, DeviceName, InitiatingProcessFileName, FolderPath, FileName, SHA256

Phase 2: Legitimate App in Wrong Location

Step 2.1 - Signed Binaries Running Outside Standard Paths

index=sysmon EventCode=1
| where NOT match(Image, "(?i)^(C:\\\\Windows|C:\\\\Program Files)")
| where match(Image, "(?i)(svchost|explorer|rundll32|dllhost|OneDrive|Teams)\.exe$")
| table _time Computer User Image CommandLine ParentImage Hashes

Phase 3: Hash-Based Detection

Step 3.1 - Known-Bad DLL Hashes

Compare loaded DLL hashes against threat intelligence:

index=sysmon EventCode=7
| rex field=Hashes "SHA256=(?<sha256>[A-Fa-f0-9]{64})"
| lookup threat_intel_hashes sha256 OUTPUT malware_family confidence
| where isnotnull(malware_family)
| table _time Computer Image ImageLoaded sha256 malware_family

Phase 4: Behavioral Correlation

Step 4.1 - Network Activity After DLL Load

Correlate DLL loads with subsequent network connections:

index=sysmon EventCode=7 Signed=false
| rename Image as proc_image
| join proc_image Computer [
    search index=sysmon EventCode=3
    | rename Image as proc_image
    | where NOT match(DestinationIp, "^(10\.|172\.|192\.168\.)")
]
| table _time Computer proc_image ImageLoaded DestinationIp DestinationPort

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