ASN-Wide Vulnerability Scan

Overview

Knowing which hosts you expose is the first half of the problem. The second half is whether any of them can be used against you. An ASN can announce thousands of addresses, and the ones that matter are rarely the ones on the asset list. They are the forgotten staging server, the appliance shipped with a default page, the service that was patched everywhere except the range nobody claims.

This workflow takes ASNs and returns findings, not just an inventory. It resolves the announced ranges through RIPEstat, port-scans them across the fleet, and runs three nuclei branches: known CVEs, exposures covering misconfiguration and default logins and takeover, and network templates against the raw ports. Destructive template classes are excluded, so this is a scan you can point at production. Output is a downloadable PDF carrying the findings, the hosts scanned, and the methodology.

Point it at your own ranges for exposure management, or at a target's ranges before a deal closes. Scheduled, it becomes regression testing for your perimeter, catching the service that reappears after a rollback.

One limit worth knowing: ASN resolution is capped at 100 prefixes per run. For an organization announcing more than that, split the ASN list across runs.

Pipeline

1. Read the targets, one per line. An ASN such as AS13335, an IP, or a CIDR. IPs and CIDRs pass straight through.
2. Targets to IP prefixes resolves each ASN to its announced ranges through RIPEstat, capped at 100 prefixes.
3. mapcidr turns those prefixes into scannable ranges.
4. rustscan port-scans them. The scan is distributed, so resolved ranges fan out across the fleet and every prefix is scanned in parallel. Results are parsed into ip:port pairs.
5. The pipeline forks here. httpx probes the pairs and keeps the ones answering as web servers, and their URLs feed two nuclei branches: CVE templates, and exposure templates covering misconfiguration, default logins and takeover.
6. In parallel, a third nuclei branch runs network templates against the raw ip:port pairs, so services that are not web servers are still tested.
7. All three branches, plus the live-host list, collect into one downloadable PDF with the findings, the hosts scanned, and the methodology.

dos, fuzz and intrusive templates are excluded, as are info-severity results.

Inputs

• Targets. One entry per line. An ASN such as AS13335 resolves to its announced ranges, while an IP or a CIDR passes straight through, so a single run can mix all three.
• Prefix cap. ASN resolution stops at 100 announced prefixes per run. That ceiling ships on, and it is what stops one large ASN from turning a run into an open-ended scan. For an organization announcing more, split the ASN list across runs.
• Template exclusions. dos, fuzz and intrusive template classes are off by default and info-severity results are dropped. Both defaults are what make this a scan you can point at production.

Outputs

• A PDF report. One downloadable file carrying the findings, the hosts scanned, and the methodology behind them.
• A live host inventory. The ip:port pairs the port scan found, plus the subset that answered as web servers with their titles, server banners and detected tech.
• Three finding sets. CVE matches, exposure matches covering misconfiguration and default logins and takeover, and network-template matches against the raw ports. Each carries the template that fired, the severity, and the address it matched on.

Sample output

From a completed run against scanme.nmap.org, the host Nmap publishes for this purpose.

httpx keeps the addresses that answer, with what is serving them:

The CVE pass reports the template, the severity, and where it matched:

CVE-2023-48795   medium   45.33.32.156:22

The exposure pass covers configuration rather than known CVEs:

apache-mod-negotiation-listing   low      http://45.33.32.156:80/index
ssh-weak-algo-supported          medium   45.33.32.156:22
ssh-diffie-hellman-logjam        low      45.33.32.156:22
ssh-cbc-mode-ciphers             low      45.33.32.156:22
ssh-weak-mac-algo                low      45.33.32.156:22

One address answered on the web, and the findings that came back are on the SSH service beside it. That is the argument for scanning the range rather than the asset list.

FAQ

Can I run this against an ASN I do not own?

The resolution step only reads public routing data, so mapping an ASN to its announced prefixes needs no permission from anyone. Everything after it is active traffic against hosts in those ranges, so run the scan itself only where you have authorization.

How is this different from running nuclei myself?

nuclei needs a target list, and building that list is most of the work here. This goes from an ASN to announced prefixes to open ports to live web servers, then runs three template sets in parallel across the fleet. The command you would have typed is step five onward.

What does a run cost?

Scope drives it. Runtime tracks the number of announced prefixes and open ports, not the number of ASNs you paste in, because the port scan is distributed and every prefix is handled at the same time. The 100-prefix cap is the ceiling on a single run.

Is it safe to point at production?

The template classes that knock services over are excluded, which is the difference between this and an unfiltered nuclei run. It is still a port scan followed by active probing, so treat it the way you would any authenticated scanner window.

What does running it on a schedule buy?

A diff. The staging box that came back after a rollback, the appliance somebody racked last week, the range that arrived with an acquisition. Compare one run against the last and the change is the finding.

Related workflows

• Find Exposed Databases. Reach for this instead when you already have the netblock and only want the data stores, checked across eight engines for anonymous access rather than swept for CVEs.
• Passive Port & CVE Scan (Shodan). Reach for this instead when you cannot scan the range yourself and need the same port and version picture out of somebody else's packets.
• Attack Surface Discovery by Company Name. Reach for this instead when you do not know which ASNs belong to the company yet and are starting from the legal name.