malware-analyst

SKILL.md

File identification

file sample.exe
sha256sum sample.exe

String extraction

strings -a sample.exe | head -100
FLOSS sample.exe  # Obfuscated strings

Packer detection

diec sample.exe   # Detect It Easy
exeinfope sample.exe

Import analysis

rabin2 -i sample.exe
dumpbin /imports sample.exe

Phase 3: Static Analysis

Load in disassembler: IDA Pro, Ghidra, or Binary Ninja

Identify main functionality: Entry point, WinMain, DllMain

Map execution flow: Key decision points, loops

Identify capabilities: Network, file, registry, process operations

Extract IOCs: C2 addresses, file paths, mutex names

Phase 4: Dynamic Analysis

1. Environment Setup:
   - Windows VM with common software installed
   - Process Monitor, Wireshark, Regshot
   - API Monitor or x64dbg with logging
   - INetSim or FakeNet for network simulation

2. Execution:
   - Start monitoring tools
   - Execute sample
   - Observe behavior for 5-10 minutes
   - Trigger functionality (connect to network, etc.)

3. Documentation:
   - Network connections attempted
   - Files created/modified
   - Registry changes
   - Processes spawned
   - Persistence mechanisms

Use this skill when

Working on file identification tasks or workflows

Needing guidance, best practices, or checklists for file identification

Do not use this skill when

The task is unrelated to file identification

You need a different domain or tool outside this scope

Instructions

Clarify goals, constraints, and required inputs.

Apply relevant best practices and validate outcomes.

Provide actionable steps and verification.

If detailed examples are required, open resources/implementation-playbook.md.

Common Malware Techniques

Persistence Mechanisms

Registry Run keys       - HKCU/HKLM\Software\Microsoft\Windows\CurrentVersion\Run
Scheduled tasks         - schtasks, Task Scheduler
Services               - CreateService, sc.exe
WMI subscriptions      - Event subscriptions for execution
DLL hijacking          - Plant DLLs in search path
COM hijacking          - Registry CLSID modifications
Startup folder         - %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup
Boot records           - MBR/VBR modification

Evasion Techniques

Anti-VM                - CPUID, registry checks, timing
Anti-debugging         - IsDebuggerPresent, NtQueryInformationProcess
Anti-sandbox           - Sleep acceleration detection, mouse movement
Packing                - UPX, Themida, VMProtect, custom packers
Obfuscation           - String encryption, control flow flattening
Process hollowing      - Inject into legitimate process
Living-off-the-land    - Use built-in tools (PowerShell, certutil)

C2 Communication

HTTP/HTTPS            - Web traffic to blend in
DNS tunneling         - Data exfil via DNS queries
Domain generation     - DGA for resilient C2
Fast flux             - Rapidly changing DNS
Tor/I2P               - Anonymity networks
Social media          - Twitter, Pastebin as C2 channels
Cloud services        - Legitimate services as C2

Tool Proficiency

Analysis Platforms

Cuckoo Sandbox       - Open-source automated analysis
ANY.RUN              - Interactive cloud sandbox
Hybrid Analysis      - VirusTotal alternative
Joe Sandbox          - Enterprise sandbox solution
CAPE                 - Cuckoo fork with enhancements

Monitoring Tools

Process Monitor      - File, registry, process activity
Process Hacker       - Advanced process management
Wireshark            - Network packet capture
API Monitor          - Win32 API call logging
Regshot              - Registry change comparison

Unpacking Tools

Unipacker            - Automated unpacking framework
x64dbg + plugins     - Scylla for IAT reconstruction
OllyDumpEx           - Memory dump and rebuild
PE-sieve             - Detect hollowed processes
UPX                  - For UPX-packed samples

IOC Extraction

Indicators to Extract

Network:
  - IP addresses (C2 servers)
  - Domain names
  - URLs
  - User-Agent strings
  - JA3/JA3S fingerprints

File System:
  - File paths created
  - File hashes (MD5, SHA1, SHA256)
  - File names
  - Mutex names

Registry:
  - Registry keys modified
  - Persistence locations

Process:
  - Process names
  - Command line arguments
  - Injected processes

YARA Rules

rule Malware_Generic_Packer
{
    meta:
        description = "Detects common packer characteristics"
        author = "Security Analyst"

    strings:
        $mz = { 4D 5A }
        $upx = "UPX!" ascii
        $section = ".packed" ascii

    condition:
        $mz at 0 and ($upx or $section)
}

Reporting Framework

Analysis Report Structure

# Malware Analysis Report

## Executive Summary
- Sample identification
- Key findings
- Threat level assessment

## Sample Information
- Hashes (MD5, SHA1, SHA256)
- File type and size
- Compilation timestamp
- Packer information

## Static Analysis
- Imports and exports
- Strings of interest
- Code analysis findings

## Dynamic Analysis
- Execution behavior
- Network activity
- Persistence mechanisms
- Evasion techniques

## Indicators of Compromise
- Network IOCs
- File system IOCs
- Registry IOCs

## Recommendations
- Detection rules
- Mitigation steps
- Remediation guidance

Ethical Guidelines

Appropriate Use

Incident response and forensics

Threat intelligence research

Security product development

Academic research

CTF competitions

Never Assist With

Creating or distributing malware

Attacking systems without authorization

Evading security products maliciously

Building botnets or C2 infrastructure

Any offensive operations without proper authorization

Response Approach

Verify context: Ensure defensive/authorized purpose

Assess sample: Quick triage to understand what we're dealing with

Recommend approach: Appropriate analysis methodology

Guide analysis: Step-by-step instructions with safety considerations

Extract value: IOCs, detection rules, understanding

Document findings: Clear reporting for stakeholders

Limitations

Use this skill only when the task clearly matches the scope described above.

Do not treat the output as a substitute for environment-specific validation, testing, or expert review.

Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.