# Ctf Malware

> Malware analysis and network traffic techniques for CTF challenges. Use when analyzing obfuscated scripts, malicious packages, custom crypto protocols, C2 traffic, PE/.NET binaries, RC4/AES encrypted communications, or extracting malware configurations and indicators of compromise.

- Skill: `njones17/ctf-malware` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add njones17/ctf-malware`
- Raw SKILL.md: https://api.skillmd.com/api/skills/njones17/ctf-malware/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: MIT
- Author: Njones17 (https://skillmd.com/u/njones17)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/njones17/ctf-malware

---


# CTF Malware & Network Analysis

Quick reference for malware analysis CTF challenges. Each technique has a one-liner here; see supporting files for full details with code.

## Additional Resources

- [scripts-and-obfuscation.md](scripts-and-obfuscation.md) - JavaScript deobfuscation, PowerShell analysis, eval/base64 decoding, junk code detection, hex payloads, Debian package analysis
- [c2-and-protocols.md](c2-and-protocols.md) - C2 traffic patterns, custom crypto protocols, RC4 WebSocket, DNS-based C2, network indicators, PCAP analysis, AES-CBC, encryption ID, Telegram bot recovery
- [pe-and-dotnet.md](pe-and-dotnet.md) - PE analysis (peframe, pe-sieve, pestudio), .NET analysis (dnSpy, AsmResolver), LimeRAT extraction, sandbox evasion, malware config extraction, PyInstaller+PyArmor

---

## Obfuscated Scripts

- Replace `eval`/`bash` with `echo` to print underlying code; extract base64/hex blobs and analyze with `file`. See [scripts-and-obfuscation.md](scripts-and-obfuscation.md).

## JavaScript & PowerShell Deobfuscation

- JS: Replace `eval` with `console.log`, decode `unescape()`, `atob()`, `String.fromCharCode()`.
- PowerShell: Decode `-enc` base64, replace `IEX` with output. See [scripts-and-obfuscation.md](scripts-and-obfuscation.md).

## Junk Code Detection

- NOP sleds, push/pop pairs, dead writes, unconditional jumps to next instruction. Filter to extract real `call` targets. See [scripts-and-obfuscation.md](scripts-and-obfuscation.md).

## PCAP & Network Analysis

```bash
tshark -r file.pcap -Y "tcp.stream eq X" -T fields -e tcp.payload
```

Look for C2 on unusual ports. Extract IPs/domains with `strings | grep`. See [c2-and-protocols.md](c2-and-protocols.md).

## Custom Crypto Protocols

- Stream ciphers share keystream state for both directions; concatenate ALL payloads chronologically.
- ChaCha20 keystream extraction: send nullbytes (0 XOR anything = anything). See [c2-and-protocols.md](c2-and-protocols.md).

## C2 Traffic Patterns

- Beaconing, DGA, DNS tunneling, HTTP(S) with custom headers, encoded payloads. See [c2-and-protocols.md](c2-and-protocols.md).

## RC4-Encrypted WebSocket C2

- Remap port with `tcprewrite`, add RSA key for TLS decryption, find RC4 key in binary. See [c2-and-protocols.md](c2-and-protocols.md).

## Identifying Encryption Algorithms

- AES: `0x637c777b` S-box; ChaCha20: `expand 32-byte k`; TEA/XTEA: `0x9E3779B9`; RC4: sequential S-box init. See [c2-and-protocols.md](c2-and-protocols.md).

## AES-CBC in Malware

- Key = MD5/SHA256 of hardcoded string; IV = first 16 bytes of ciphertext. See [c2-and-protocols.md](c2-and-protocols.md).

## PE Analysis

```bash
peframe malware.exe      # Quick triage
pe-sieve                 # Runtime analysis
pestudio                 # Static analysis (Windows)
```

See [pe-and-dotnet.md](pe-and-dotnet.md).

## .NET Malware Analysis

- Use dnSpy/ILSpy for decompilation; AsmResolver for programmatic analysis. LimeRAT C2: AES-256-ECB with MD5-derived key. See [pe-and-dotnet.md](pe-and-dotnet.md).

## Malware Configuration Extraction

- Check .data section, PE/.NET resources, registry keys, encrypted config files. See [pe-and-dotnet.md](pe-and-dotnet.md).

## Sandbox Evasion Checks

- VM detection, debugger detection, timing checks, environment checks, analysis tool detection. See [pe-and-dotnet.md](pe-and-dotnet.md).

## PyInstaller + PyArmor Unpacking

- `pyinstxtractor.py` to extract, PyArmor-Unpacker for protected code. See [pe-and-dotnet.md](pe-and-dotnet.md).

## Telegram Bot Evidence Recovery

- Use bot token from malware source to call `getUpdates` and `getFile` APIs. See [c2-and-protocols.md](c2-and-protocols.md).

## Debian Package Analysis

```bash
ar -x package.deb && tar -xf control.tar.xz  # Check postinst scripts
```

See [scripts-and-obfuscation.md](scripts-and-obfuscation.md).

## Network Indicators Quick Reference

```bash
strings malware | grep -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
tshark -r capture.pcap -Y "dns.qry.name" -T fields -e dns.qry.name | sort -u
```