I built a non-destructive attack surface scanner in Python — here's what real targets taught me

gevar — Tue, 10 Nov 2026 06:50:23 +0000

I built a non-destructive attack surface scanner in Python — here's what real targets taught me

AttackSurfaceX (ASX) is an open-source, CLI-first attack surface scanner with one hard design rule: it must never be able to hurt the target. No exploits, no fuzzing payloads, no write operations — detection only, behind a strict scope gate.

pipx install git+https://github.com/gevarru/AttackSurfaceX.git
asx scan -t https://example.com -p safe

Why "non-destructive" is the whole point

Most recon tools assume you trust yourself. ASX assumes you'll run it against production systems at 2 AM. That drove three architectural decisions:

1. Scope enforcement before anything else. Nothing is scanned unless it's declared in scope.yaml. Wide scans require an explicit flag. The scanner refuses to even resolve a host outside the declared scope.

2. A plugin safety gate. Plugins are third-party Python, so the loader statically inspects imports — a plugin that touches os, subprocess, or raw socket is refused before it ever runs.

3. GET/HEAD only. The HTTP layer physically cannot send state-changing requests. Rate-limited, self-identifying User-Agent, fixed timeouts.

Modules: asyncio TCP port scan with banner grabbing, a TLS audit (cert chain, deprecated protocol detection — read-only handshakes), web checks (security headers, cookie flags, CORS, version disclosure, exposed sensitive paths, inert reflected-XSS canaries), a YAML rules engine, and reporters for JSON / Markdown / interactive HTML / SARIF (GitHub Code Scanning). MIT licensed, Python 3.11+.

What real targets actually taught me

I want this part to be honest, because most "I built a scanner" posts only show the happy path. Here's what happened when ASX met real, hardened perimeters.

Lesson 1: Geo-blocking is indistinguishable from TLS failure — and your scanner will lie about it.
The first real run was against a major fintech. Every port "closed", TLS handshake "failed", HTTP "unreachable". It looked like a finding (CWE-326, medium). In reality, the target silently drops connections from certain countries at the CDN edge. The packets never arrived. The scanner wasn't measuring the target's security — it was measuring my network position.

Fix in progress: a dedicated target-unreachable/filtered finding type, triggered when TCP fails across the entire port set and TLS never completes. If your scanner can't tell "firewalled" from "broken crypto", it will file false reports — and in a bug bounty context, false reports are reputation damage.

Lesson 2: Modern SPAs return HTTP 200 for everything.
Exposed-path scanning (/.git/HEAD, /.env, /swagger.json) hits a wall: single-page apps serve the index HTML with a 200 for any path. Naive checking produced dozens of "exposed .git" hits that were all the same 12 KB of HTML. The discriminator is content variance — real endpoints differ in size and type from the catch-all shell. The same host that shows 200 for /backup.zip will 401 or 404 for the real thing once you follow the variance.

Lesson 3: Failed handshakes leak sockets — the edge that filters you also exhausts you.
Same geo-block scenario, second bug — and this one was in my code, not theirs. The TLS probe used to look like this:

raw = socket.create_connection((host, port), timeout=timeout)
ssock = ctx.wrap_socket(raw, server_hostname=host)

When wrap_socket fails mid-handshake — precisely what a silently-filtering edge does — the exception path returned early and the raw socket was never closed. One leaked fd per failed probe: harmless in a five-target scan, a slow exhaustion in a wide recon run. The fix is ownership discipline: clear the raw reference once the TLS socket takes over, and close it in finally if it never did. (Found by reading the code paths the geo-block run exercised; fixed in commit d8ccc5f.)

The verdict after the first recon runs

Against top-tier perimeters (large fintech, food delivery platform), ASX found zero reportable vulnerabilities from the outside. That is the correct result — mature programs are externally clean. The scanner's value isn't finding magic bugs in port 443; it's mapping the surface cheaply and safely so human effort can go where bugs actually live: authenticated application logic.

Roadmap

CSRF & form-analysis module
Session/authenticated scanning helpers
SBOM / supply-chain scanning (OSV integration)
Resume support for long scans
target-unreachable classification (Lesson 1)

Try it

git clone https://github.com/gevarru/AttackSurfaceX.git
cd AttackSurfaceX
pip install -e .
python -m asx.cli scan -t https://your-own-domain.com -p safe

Only scan what you own or are authorized to test. ASX detects indicators — it never exploits them.

⭐ github.com/gevarru/AttackSurfaceX

DEV Community: gevar

I built a non-destructive attack surface scanner in Python — here's what real targets taught me

I built a non-destructive attack surface scanner in Python — here's what real targets taught me

Why "non-destructive" is the whole point

What real targets actually taught me

The verdict after the first recon runs

Roadmap

Try it