Malware Triage

First phase for every sample. You run static tools on the host, interpret the output, classify the sample, and decide the next phase. Target: 5-15 minutes per sample.

Execution Model

• You run the commands. You have Bash. Execute every command in this skill yourself and interpret the output. Do not ask the user to run tools or paste results unless a tool is missing and cannot be installed.
• Locate skill files. Scripts and reference files ship in this skill's directory. Set R="${CLAUDEPLUGINROOT:-<dir containing this SKILL.md>}" once (when installed as a plugin $CLAUDEPLUGINROOT is set; otherwise it is this skill folder). Your working directory is the user's analysis workspace, so prefix every script path below with $R, e.g. python3 "$R"/scripts/ioc_extract.py.
• Never execute the sample. Only static tools touch it: file, strings, pe_info.py, upx -d, 7z l, hashing. No chmod +x, no wine, no ./sample.
• Never upload the sample to any service without explicit consent. Hash lookups are fine; file uploads are not.
• Script paths are relative to this skill directory. From the repo/skill root: malware-triage/scripts/peinfo.py, malware-triage/scripts/hashcalculator.py, scripts/ioc_extract.py. Resolve them from wherever this SKILL.md lives.
• Tool check first. Run once per session; note what is missing and degrade rather than stop:

``bash command -v file strings upx 7z yara; python3 -c "import pefile" 2>&1 | tail -1 # pefile missing -> pip install pefile (needed by pe_info.py) ``

• Big outputs: never cat a strings dump. Save to a file, wc -l, then grep/head.
• Ask the user only for: the sample path, context (where it came from, incident ID, anything already known), and reputation results if no MCP server is available.

Workflow

Step 1 — Identify and hash

S=/path/to/sample
file "$S"; ls -l "$S"
python3 malware-triage/scripts/hash_calculator.py "$S"

Record MD5/SHA1/SHA256, size, file output. Then route on the file output:

Step 2 — Reputation

• MCP available (VirusTotal, Threat Intel / MalwareBazaar): look up the SHA256. Record detection ratio, family labels, first-seen date, tags. Look up any imphash and section hashes too.
• No MCP: give the user the SHA256 and ask them to check VirusTotal / MalwareBazaar while you continue. Do not block on it. Zero detections on a fresh hash means nothing; 0 detections on an old hash is informative.
• Reputation is a hint, not the verdict. Static findings override AV labels.

Step 3 — PE static summary

python3 malware-triage/scripts/pe_info.py "$S"          # add --json for structured output

Read every section of the output. What matters:

Step 4 — Strings and IOCs

W=triage_$(basename "$S")   # work dir
mkdir -p "$W"
strings -a -n 6 "$S"      > "$W/strings_ascii.txt"
strings -a -n 6 -e l "$S" > "$W/strings_wide.txt"      # UTF-16LE, essential for Windows binaries
wc -l "$W"/strings_*.txt
python3 scripts/ioc_extract.py "$W"/strings_*.txt         # defanged IPs, domains, URLs, emails, hashes, reg keys, paths

Then targeted greps (adjust after reading the ioc_extract output):

grep -ihE 'HKEY_|HKLM|HKCU|CurrentVersion\\Run|schtasks|sc create|netsh|vssadmin|bcdedit|wmic' "$W"/strings_*.txt | sort -u | head -40
grep -ihE 'user-agent|mozilla/|POST |GET |Content-Type|\.php|\.onion|/gate|/panel' "$W"/strings_*.txt | sort -u | head -40
grep -ihE 'mutex|Global\\|Local\\|\\pipe\\' "$W"/strings_*.txt | sort -u | head -20
grep -ihE 'IsDebuggerPresent|VMware|VBox|vbox|QEMU|Xen|sandbox|SbieDll|wireshark|procmon|ollydbg|x64dbg' "$W"/strings_*.txt | sort -u
grep -ihE 'bitcoin|monero|\.onion|decrypt|ransom|your files|README' "$W"/strings_*.txt | sort -u | head -20
grep -ihE '\.exe|\.dll|\.bat|\.ps1|\.vbs|\.tmp' "$W"/strings_*.txt | grep -viE 'kernel32|ntdll|user32|advapi32|msvcr|api-ms-win' | sort -u | head -40

Note what is absent too: a binary with network imports but no URL/IP strings is decrypting its config at runtime.

Suspicious-API and string categories: references/indicators.md.

Packed Samples

Triggered by Step 3 entropy/import findings.

If UPX unpacking succeeds: hash the unpacked file, re-run Steps 3-4 on it, record both hashes (packed = delivery artifact, unpacked = what matches families). If upx -d fails, the UPX header was tampered; treat as custom.

Set sophistication: known packer → at least Moderate; commercial protector → Advanced; custom packer → Advanced/APT. Add "requires dynamic analysis to reveal imports/strings" to next steps.

Step 5 — Classify

Combine imports, strings, reputation, and context. Consult references/indicators.md for the patterns.

Threat level: Critical (destructive, ransomware, APT) / High (data theft, full compromise) / Medium (limited capability, targeted) / Low (adware, PUP, commodity). Sophistication: Simple / Moderate / Advanced / APT-level, driven by protection, evasion, and custom code. Verdict: Malicious / Suspicious / Benign. Benign requires positive evidence (valid signature from a plausible vendor, expected imports for its stated purpose, reputation clean over time), not just absence of red flags.

Step 6 — Predict behavior

Turn static evidence into a watch list for the dynamic phase. Each prediction names the evidence:

• Process: child processes or injection expected? Which targets (CreateRemoteThread + OpenProcess → injection; CreateProcess + cmd/powershell strings → LOLBin chain)?
• Files: paths from strings; temp/AppData drops if GetTempPath/SHGetFolderPath imported.
• Registry: Run keys, service creation, IFEO from strings/imports.
• Network: protocol (WinHTTP/WinINet → HTTP(S); socket/connect → raw TCP; DnsQuery only → DNS tunnelling/DGA), hard-coded C2 vs runtime-decrypted, likely beacon.
• Persistence: mechanism and location.
• Evasion: anti-VM/anti-debug strings → plan for bypass (malware-dynamic-analysis/references/antianalysisbypass.md).

These predictions become the Procmon/Sysmon filters and the observation plan for malware-dynamic-analysis.

Step 7 — Priority and next phase

Next phase: malware-dynamic-analysis for PE files that are packed, have runtime-resolved config, or need behavioral confirmation; detection-engineer + malware-report-writer directly when the sample is a known variant and static IOCs suffice; Benign closes the sample.

Unknown Files

file returned data or something unhelpful:

xxd "$S" | head -20                      # magic bytes, structure
strings -a -n 8 "$S" | head -50
python3 - "$S" <<'EOF'                   # single-byte XOR brute force for a hidden PE
import sys; b=open(sys.argv[1],'rb').read()
for k in range(1,256):
    d=bytes(x^k for x in b[:4096])
    if d[:2]==b'MZ' or b'This program cannot' in d: print(f"XOR key 0x{k:02x} reveals PE header")
EOF

Also check: base64 blob ([A-Za-z0-9+/]{100,}), gzip/zlib magic (1f 8b, 78 9c), reversed PE (ZM at end), shellcode (starts with fc e8 / e8 00 00 00 00 / 55 8b ec). Decode what you find, file the result, and re-route.

Batch Triage

For N samples, do a quick pass on all before deep-diving any:

for f in samples/*; do
  echo "== $f"; file "$f"; sha256sum "$f"
  python3 malware-triage/scripts/pe_info.py "$f" 2>/dev/null | grep -E '^\.NET:|packed|imported functions' 
done

Produce a ranking table (sample, type, packed, detections, priority, one-line reason), then run the full workflow on Immediate samples first.

Output

1. Print the triage report (template below, filled in — no placeholders left).
2. Append to analysis_state.md in the user's working directory using the orchestrator's structure: hashes, type, priority, classification, threat level, triage findings, IOCs (defanged), next-phase recommendation.
3. Recommend the next phase with reasoning, then wait for the user.

## Triage Report — [filename]

**Hashes:** MD5 … / SHA1 … / SHA256 …   **Size:** … bytes   **Type:** …   **Packed:** No | Yes (packer)
**Reputation:** VT x/y, family label(s), first seen … | not checked

### Static Findings
- Compile time / linker / signature / PDB
- Sections + entropy (flag anomalies)
- Suspicious imports by category → capability
- Notable strings: URLs, IPs, paths, registry, mutex, UA, commands
- Resources / overlay / TLS callbacks

### Classification
**Verdict:** Malicious | Suspicious | Benign   **Type:** …   **Threat:** Critical | High | Medium | Low   **Sophistication:** …
**Capabilities:** …

### Predicted Behavior
Process / Files / Registry / Network / Persistence / Evasion — each with the evidence behind it

### Initial IOCs (defanged)
File: hashes, imphash, dropped names · Network: … · Host: registry, paths, mutex

### Recommendation
**Priority:** …   **Next phase:** …   **Why:** …

Quality Gate

Before handing back: all three hashes; file type; packing status with evidence; imports categorized; strings run in both ASCII and UTF-16; IOCs extracted and defanged; classification with reasoning; predictions tied to evidence; state file updated.

References

• references/indicators.md — suspicious API imports, string patterns, behavioral indicators, packer signatures, classification patterns
• references/triage_checklist.md — full checklist, decision tree, dynamic go/no-go criteria, tool reference
• scripts/pe_info.py — PE header/section/import/resource/overlay/signature summary (needs pefile)
• scripts/hash_calculator.py — MD5/SHA1/SHA256
• ../scripts/ioc_extract.py — IOC extraction and defanging from any text