A SOC analyst's notes on going from "I want to learn async" to a working tool that other analysts can clone and use.

TL;DR

I'm a SOC analyst learning Python and built IOC Hunter — an async tool that takes a chunk of text (phishing report, log dump, Slack export), extracts every indicator inside, queries six threat-intel sources in parallel, and produces a verdict you can drop into a ticket or a SIEM.

This article is the why and the how — the architectural decisions I had to think through, the things that bit me, and a small dose of "what I learned about myself as an engineer."

The Problem

I sit in a SOC. The shape of my day is: alert fires → triage → mostly boring → occasionally interesting → write a ticket.

The "occasionally interesting" part is where I noticed the same workflow repeating. Someone forwards me a phishing email. The body has IPs, URLs, hashes, an email address. Half of them are defanged (evil[.]com, hxxps://, bad[at]evil[.]com). Some are encoded — base64 in the headers, hex in the payload.

To triage, I do roughly this:

1. Refang each indicator by hand
2. Open VirusTotal, paste
3. Open AbuseIPDB, paste
4. Open URLhaus, paste
5. Mentally aggregate "VT says X, AbuseIPDB says Y, URLhaus has it as Z"
6. Decide
7. Write the ticket, paraphrasing the sources

This is a 30-minute manual process for what should be 30 seconds. And most existing IOC checkers I found on GitHub were 1:1: one IOC in, one source out. They didn't solve the workflow problem — they just slightly automated step 2.

So I wrote one that solves the whole thing.

What it actually does

$ ioc-hunter check "185[.]220[.]101[.]42"

Output (simplified):

╭─────── IOC Hunter ────────╮
│ 185[.]220[.]101[.]42      │
│ type: ipv4                │
│                           │
│ MALICIOUS  confidence 46% │
╰───────────────────────────╯

Source       Verdict      Score   Notes
─────────────────────────────────────────────
tor_exit     SUSPICIOUS    0.50   tor, anonymizer
abuseipdb    MALICIOUS     1.00   country:DE, isp:Tor-Exit traffic
otx          MALICIOUS     1.00   Bruteforce, SSH, Honeypot
virustotal   MALICIOUS     0.15   suspicious-udp, tor
urlhaus      UNKNOWN       0.00
threatfox    UNKNOWN       0.00

Six sources, queried in parallel, defanged on input and on output (so you can paste the result into a chat without anyone clicking it), weighted verdict with the per-source contribution shown explicitly so you can defend the call in a ticket.

But the real feature is scan-file — drop in a 200-line incident report, get back every indicator inside, each enriched, sorted by confidence. And correlate finds the pivots: shared infrastructure, shared malware tags, URL-to-host relationships across the batch.

Architectural Decisions That Took Thought

1. The plugin pattern for sources

I want adding a new TI feed to be one file, no other changes anywhere.

class Source(ABC):
    name: str
    weight: float
    supported_types: frozenset[IOCType]
    requires_key: bool = False

    @abstractmethod
    async def lookup(self, ioc_type: IOCType, ioc_value: str) -> SourceResult:
        ...

Each source is a class with class-level metadata (weight, supported_types, requires_key) and one method. The orchestrator introspects the metadata to pick which sources to query for each IOC and to skip ones whose key isn't configured.

This means I can drop in a Shodan source tomorrow and not touch the engine, scorer, or CLI.

2. Graceful degradation > opinionated requirements

A naive design: "no API keys → tool doesn't work." A user-friendly design: every source short-circuits to UNKNOWN if its key is missing, with an explanatory error message; the rest run normally.

@property
def is_configured(self) -> bool:
    return not self.requires_key or bool(self._api_key)

The orchestrator skips unconfigured sources before they ever fire a request. So if you clone my repo and run it without registering for anything, you still get a verdict — just from the one truly-keyless source (Tor exit list). Five API keys unlock the rest.

This is the difference between "demo project" and "tool people actually try." Anyone cloning it sees output in 30 seconds.

3. Transparent weighted scoring, not a black box

Every verdict comes with the per-source contribution. The scoring formula is:

weighted: dict[Verdict, float] = dict.fromkeys(Verdict, 0.0)
for r in valid_results:
    w = sources_by_name[r.source].weight
    if r.verdict in {MALICIOUS, SUSPICIOUS}:
        weighted[r.verdict] += w * max(r.score, MIN_PRESENCE_SCORE)
    elif r.verdict is BENIGN:
        weighted[r.verdict] += w

Then severity-prioritized thresholds (malicious share ≥ 25% wins, etc.).

The whole function is 30 lines. An analyst can read it and reproduce the verdict on paper. That matters when defending a finding in an incident review.

4. Async concurrency with a global cap

class Engine:
    def __init__(self, sources, *, cache=None, max_concurrency=8):
        self._sem = asyncio.Semaphore(max_concurrency)

    async def _lookup_cached(self, ioc, source):
        if self._cache and (hit := self._cache.get(...)):
            return hit
        async with self._sem:
            return await source.lookup(...)

The semaphore is shared across all sources and all IOCs. So when the analyst feeds in 100 IOCs, the engine doesn't slam every source with 100 simultaneous requests — it pipelines them through the cap.

The free tiers of these APIs have rate limits (VirusTotal: 4 req/minute on free). Without the cap I'd hit 429s instantly.

Things That Bit Me

URLhaus and ThreatFox now require auth

Until mid-2024 they were truly keyless. The abuse.ch team added Auth-Key requirement to fight scraper abuse. The key is free and registration is instant, but my "everything-keyless" pitch had to become "Tor-keyless, everything else free signup."

This is fine, but it taught me to always link to the registration URL from the error message when a source short-circuits. Don't make the user dig.

VirusTotal URL IDs are not URLs

VT's v3 API expects URLs as urlsafe-base64(url) with padding stripped. I lost an hour to this before reading their docs carefully:

def _vt_url_id(url: str) -> str:
    return base64.urlsafe_b64encode(url.encode()).rstrip(b"=").decode()

Rich's markup parser eats [@]

I render defanged values in the CLI: bad@evil.com → bad[@]evil[.]com. Rich's table renderer interpreted [@] as a (nonexistent) markup tag and silently stripped it. Output became badevil[.]com — completely broken.

The fix is rich.markup.escape():

def _safe(value: str) -> str:
    return rich.markup.escape(defang(value))

I now wrap every IOC value in _safe() before passing to a Rich component. Tests caught this only after I started writing the README — the tests verified the verdict, not the rendered string.

STIX 2.1 patterns need apostrophe-escaping

A domain IOC with an apostrophe (it's.example.com — weird but possible) breaks the STIX pattern:

[domain-name:value = 'it's.example.com']  ← invalid
[domain-name:value = 'it\'s.example.com'] ← valid

Pattern values are single-quoted in STIX, so embedded apostrophes need escaping. Took a tracked-down-on-purpose test to catch it.

The Boring Parts That Matter

If you read GitHub-shaped engineering posts, the "boring parts" — tests, CI, lint, secret scanning, Docker hygiene — get one sentence at the end. They probably deserve half the post.

217 unit tests. Every regex pattern, every source, every exporter, every scorer threshold has a test. Network is mocked via respx. The test suite runs in 0.7 seconds. I can refactor anything and know within a second if I broke something.

CI matrix. Tests run on Python 3.11 and 3.12. Ruff lints and format-checks. Docker image builds. Gitleaks scans the diff for accidentally-committed secrets. Every PR has to pass all of this before merging.

Multi-stage Docker. The runtime image is non-root, ~120 MB, doesn't include test files or the wheel-builder layer. The cache directory is a mounted volume so it survives container restarts.

None of this is impressive on its own. It's the table stakes that separates "code I'd hire someone for" from "code I'd ask them to explain in an interview."

What I Learned About Myself

I started this thinking "I'll learn asyncio." I finished thinking "asyncio was the easy part — the hard part was deciding what not to build."

Half the work was saying no:

• No PyYAML for Sigma generation. Hand-write the YAML, save a dependency.
• No SQLAlchemy for the cache. Stdlib sqlite3 is enough.
• No "agent framework" for plugin sources. An ABC and a list is enough.
• No background daemon. A CLI is enough.
• No web UI. The Rich TUI is enough.

Every "is enough" is a thing I didn't have to test, document, maintain, or explain to a hiring manager. The project is 6,000 lines of code and 4 runtime dependencies because of that discipline.

I think this is the real seniority signal. Anyone can add a dep. Not everyone can leave one out.

If You Want to Try It

git clone https://github.com/platinum2high/ioc-hunter
cd ioc-hunter
python -m venv .venv && source .venv/bin/activate
pip install -e .

ioc-hunter check "185[.]220[.]101[.]42"   # works keyless
ioc-hunter configure                       # walks through optional API keys
ioc-hunter scan-file examples/sample-incident.txt

Or with Docker:

cp .env.example .env
docker compose run --rm ioc-hunter check evil[.]com

The repo is MIT, the issue tracker is open, and I'd genuinely love feedback from SOC analysts on the scoring model, defang patterns, and sources I should add. (I'm thinking abuse.ch MalwareBazaar and GreyNoise next.)

Code: github.com/platinum2high/ioc-hunter

Reach me on LinkedIn if you want to chat about SOC tooling, threat intel, or detection engineering.