# Reverse Engineering Dotnet Malware With Dnspy

> Use when reverse engineers .NET malware using dnSpy decompiler and debugger to analyze C#/VB.NET source code, identify obfuscation techniques, extract configurations, and understand malicious functionality including stealers, RATs, and loaders. Activates for requests involving .NET malware analysis, C# malware decompilation, managed code reverse engineering, or .NET obfuscation analysis. . Use when working with reverse engineering dotnet malware with dnspy.

- Skill: `oyi77/reverse-engineering-dotnet-malware-with-dnspy` (Agent Skill)
- Install (CLI): `npx skillmds add oyi77/reverse-engineering-dotnet-malware-with-dnspy`
- Raw SKILL.md: https://api.skillmd.com/api/skills/oyi77/reverse-engineering-dotnet-malware-with-dnspy/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: Apache-2.0
- Author: oyi77 (https://skillmd.com/u/oyi77)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/oyi77/reverse-engineering-dotnet-malware-with-dnspy

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# Reverse Engineering Dotnet Malware With Dnspy

## Overview

Cybersecurity skill for reverse engineering dotnet malware with dnspy. Follows industry best practices and security standards.

## When to Use
**Trigger phrases:**
- "reverse engineering dotnet malware with dnspy"
- "reverseing engineering dotnet malware with dnspy"
- "Reverse engineers "


- A malware sample is identified as a .NET assembly (C#, VB.NET, F#) requiring decompilation
- Analyzing .NET-based malware families (AgentTesla, AsyncRAT, RedLine Stealer, Quasar RAT)
- Deobfuscating .NET code protected by ConfuserEx, SmartAssembly, or custom obfuscators
- Extracting hardcoded C2 configurations, encryption keys, and credentials from managed assemblies
- Debugging .NET malware at runtime to observe decryption routines and dynamic behavior

**Do not use** for native (unmanaged) PE binaries; use Ghidra or IDA for native code analysis.


## When NOT to Use

- When you lack proper authorization for testing
- For production systems without change management
- When the task requires legal or compliance expertise beyond technical scope


## Prerequisites

- dnSpy or dnSpyEx installed (https://github.com/dnSpyEx/dnSpy - community maintained fork)
- de4dot for automated .NET deobfuscation (`https://github.com/de4dot/de4dot`)
- ILSpy as an alternative decompiler for cross-validation
- .NET SDK installed for recompiling modified assemblies during analysis
- Isolated Windows VM for running dnSpy debugger on live malware
- Detect It Easy (DIE) for identifying the .NET obfuscator used

## Workflow

```python
# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}
```

1. **Define Objectives** — Clarify the goals and scope for engineering dotnet malware.
2. **Gather Resources** — Collect tools, data, and access needed for engineering dotnet malware.
3. **Execute Process** — Carry out engineering dotnet malware operations methodically.
4. **Verify Quality** — Check results against acceptance criteria.
5. **Document Outcomes** — Record findings, decisions, and next steps.

## Tools

- **dnspy** — Primary tool for this skill
- **Analysis Platform** — Data processing and visualization
- **Collaboration Tools** — Team coordination and knowledge sharing


## Process

1. **Reconnaissance** — Gather target information, identify attack surface, enumerate services
1. **Analysis/Exploitation** — Execute the technique, analyze results, document findings
1. **Reporting** — Document IOCs, write findings, provide remediation recommendations

## Verification

- [ ] All engineering dotnet malware procedures executed completely and documented
- [ ] Findings validated against multiple data sources
- [ ] False positives identified and filtered
- [ ] Results documented with evidence and timestamps
- [ ] Recommendations provided with risk-based prioritization

## Anti-Rationalization Table

| Rationalization | Reality |
|---|---|
| "We are too small to be targeted" | Automated attacks target everyone. Size does not matter. |
| "Security slows us down" | A breach slows you down 100x more. Build security in from the start. |
| "We will fix it after launch" | Vulnerabilities in production are exploited within hours. Fix before deploy. |