Advanced String Hunt
Extract the C2 URL, persistence key, and mutex name from a binary using string analysis.
Investigate
Hints
Hint 1
Open the file in the hex viewer and read the ASCII column.
Hint 2
The strings are not in a standard PE section — scan the whole file.
Hint 3
The file is 8KB of realistic filler around three real strings — Find is faster than scrolling. The URL sits around offset 0xC40, the persistence path around 0x1420, the mutex around 0x1B90.
Submit Findings
Solution
Advanced String Hunt — Solution
The binary plants three telling strings inside 8KB of realistic filler — nothing is visible without scrolling or searching:
- C2 URL:
http://malware-c2.xyz/gate.php(offset 0xC40) — the command-and-control endpoint. - Persistence key:
Software\Microsoft\Windows\CurrentVersion\Run(offset 0x1420) — the classic autostart location. - Mutex:
Global\mx_0x1A2B3C(offset 0x1B90) — a single-instance guard so only one copy runs.
Methodology: a URL + a Run key + a mutex together describe a program that phones home, persists, and avoids duplicates — a textbook implant profile. Use the hex viewer's Find to jump straight to each string rather than scrolling byte by byte.
Prerequisites
- sa1-strings-metadata
- Hex editor usage
- Common malware IOC patterns (C2, mutex, Run keys)
Methodology
Investigation Methodology
1. Load & Scan
- Open the binary in the hex viewer or a hex editor
- Enable ASCII/UTF-8 column view
- Scroll through the entire file — raw binaries have no section structure
2. Identify IOC Categories
Look for these telltale patterns:
| Category | Patterns | Example |
|---|---|---|
| C2/Network | http://, https://, IP addresses, domains |
http://c2.example.com/gate.php |
| Persistence | Run, RunOnce, Services, Startup, Winlogon |
Software\Microsoft\Windows\CurrentVersion\Run |
| Mutex | Global\, Local\, Mutex, MUTEX |
Global\mx_123 |
| File Paths | %APPDATA%, %TEMP%, %SYSTEM%, \\.\ |
%APPDATA%\svchost.exe |
| Crypto | AES, RSA, RC4, XOR, base64 strings |
U2FsdGVkX1... |
3. Extract & Document
- Note the file offset of each string
- Record the full string exactly as it appears
- Categorize each finding
- Build the behavioral profile
4. Correlate Findings
- C2 URL + Persistence + Mutex = Implant/Beacon
- C2 URL only = Downloader/Stage 1
- Persistence + File drop = Dropper
- Mutex only = Single-instance component (part of larger malware)
5. Pivot to Deeper Analysis
- Use C2 domain for infrastructure hunting (VirusTotal, URLhaus)
- Use mutex for host-based detection
- Use persistence path for registry monitoring
Common Pitfalls
- Only running `strings` with default minimum length (4 chars) — misses short IOCs
- Assuming PE section structure in a raw binary blob
- Missing Unicode/UTF-16 strings — always check both ASCII and wide char
- Overlooking environment variable paths (`%APPDATA%`, `%TEMP%`)
- Not noting file offsets — needed for YARA rules and precise detection
Tools
- Built-in Hex Viewer
- strings (GNU) with `-a` (all) and `-el` (UTF-16LE) flags
- FLOSS (FireEye) for obfuscated string extraction
- Ghidra (Defined Strings window)
- ImHex / HxD / 010 Editor
References
- Lesson SA1: Strings & Metadata
- MITRE ATT&CK: T1071 (C2), T1547 (Persistence), T1543 (Mutex)
- Malware IOC standards: STIX, OpenIOC, MISP
- FireEye FLOSS documentation
Extensions & Challenges
- Write a YARA rule matching all three IOCs
- Extract strings from a real sample (MalwareBazaar) and categorize
- Research: How do malware authors encode/encrypt strings to evade `strings`?
- Build a string extractor that handles XOR, ROT, base64, and custom encodings