Ctf•恶意软件分析 Agent Skill

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.

Prerequisites

Python packages (all platforms):

pip install yara-python pefile capstone oletools unicorn pycryptodome \
  volatility3 dissect.cobaltstrike

Linux (apt):

apt install strace ltrace tshark binwalk binutils

macOS (Homebrew):

brew install wireshark binwalk binutils ghidra

Manual install:

• dnSpy — GitHub, .NET decompiler (Windows)

Additional Resources

• scripts-and-obfuscation.md - JavaScript deobfuscation, PowerShell analysis, eval/base64 decoding, junk code detection, hex payloads, Debian package analysis, dynamic analysis techniques (strace/ltrace, network monitoring, memory string extraction, automated sandbox execution), YARA rules for malware detection, shellcode analysis (Unicorn Engine, Capstone), memory forensics for malware (Volatility 3 malfind, process injection detection), anti-analysis techniques (VM detection, timing evasion, API hashing, process injection), trojanized plugin analysis with custom alphabet C2 decoding
• 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, Poison Ivy RAT Camellia decryption
• pe-and-dotnet.md - PE analysis (peframe, pe-sieve, pestudio), .NET analysis (dnSpy, AsmResolver), LimeRAT extraction, sandbox evasion, malware config extraction, PyInstaller+PyArmor

When to Pivot

• If the sample is really just a normal crackme, packed challenge binary, or custom VM with no malware behavior, switch to /ctf-reverse.
• If the main job is network reconstruction, disk carving, or host artifact recovery, switch to /ctf-forensics.
• If the challenge turns into public attribution or infrastructure tracing, switch to /ctf-osint.

Quick Start Commands

# Static analysis
file suspicious_file
strings -n 8 suspicious_file | head -50
xxd suspicious_file | head -20

# PE analysis
python3 -c "import pefile; pe=pefile.PE('mal.exe'); print(pe.dump_info())" | head
peframe mal.exe

# Dynamic analysis (sandboxed!)
strace -f -s 200 ./suspicious 2>&1 | head -100
ltrace ./suspicious 2>&1 | head -50

# Network indicators
strings suspicious_file | grep -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
strings suspicious_file | grep -iE 'http|ftp|ws://'

# YARA scan
yara -r rules.yar suspicious_file

Obfuscated Scripts

• Replace eval/bash with echo to print underlying code; extract base64/hex blobs and analyze with file. See 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.

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.

PCAP & Network Analysis

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.

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 Traffic Patterns

• Beaconing, DGA, DNS tunneling, HTTP(S) with custom headers, encoded payloads. See 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.

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.

AES-CBC in Malware

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

PE Analysis

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

See 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.

Malware Configuration Extraction

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

Sandbox Evasion Checks

• VM detection, debugger detection, timing checks, environment checks, analysis tool detection. See pe-and-dotnet.md.

Anti-Analysis Techniques

VM detection (CPUID, MAC prefix, registry, disk size), timing evasion (sleep/RDTSC sandbox detection), API hashing (ROR13/DJB2/CRC32 + hashdb lookup), process injection (hollowing, APC, CreateRemoteThread), environment checks. See scripts-and-obfuscation.md.

Trojanized Plugin Analysis

Diff malicious plugin against official release to find injected code in try/except blocks. Custom alphabet rotation (C(C.index(ch) - offset) % len(C)]) decodes C2 domain, XOR decodes endpoint path. See [scripts-and-obfuscation.md.

PyInstaller + PyArmor Unpacking

• pyinstxtractor.py to extract, PyArmor-Unpacker for protected code. See 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.

Debian Package Analysis

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

See scripts-and-obfuscation.md.

YARA Rules for Malware Detection

Write YARA rules to match byte patterns, strings, and regex against files or memory dumps. Detect XOR loops ({31 ?? 80 ?? ?? 4? 75}), base64 blobs, encoded PowerShell. Use yarac to compile for faster scanning. See scripts-and-obfuscation.md.

Shellcode Analysis

Disassemble with objdump -b binary -m i386:x86-64, emulate with Unicorn Engine (hook syscalls safely), or use Capstone for programmatic disassembly. Look for XOR decoder stubs. See scripts-and-obfuscation.md.

Memory Forensics for Malware

vol3 windows.malfind detects injected code (PAGE_EXECUTE_READWRITE without mapped file). windows.pstree reveals suspicious parent-child relationships. YARA scan memory with yarascan.YaraScan. See scripts-and-obfuscation.md.

Network Indicators Quick Reference

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