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Cloudflare Open-Sources Network Vulnerability Scanner

Security and web performance services provider Cloudflare this week announced the open source availability of Flan Scan, its lightweight network vulnerability scanner.

Based on the Nmap open source tool, Flan Scan was born out of the need for an easy-to-deploy scanner that could accurately detect the services on a network and then look them up in a database of CVEs to find any relevant vulnerabilities.

Cloudflare chose Nmap as the base scanner due to its focus on reducing false positives and because the Nmap Scripting Engine (NSE) allows scripts to be run against the scan results. Moreover, the “vulners” script on NSE would already map detected services to relevant CVEs from a database.


To convert Nmap to Flan Scan, Cloudflare added three features: Easy Deployment and Configuration — Flan Scan runs inside a Docker container and also includes sample Kubernetes configuration and deployment files — support for pushing results to a Google Cloud Storage Bucket or an S3 bucket, and Actionable Reports generated from Nmap’s output.

The protection services provider claims that Flan Scan has already helped it complete compliance scans and improve the security of its network through discovering the use of an outdated, vulnerable version of Apache, and a vulnerable instance of PostgreSQL.

“Flan Scan is part of a larger effort to expand our vulnerability management program. We recently deployed osquery to our entire network to perform host-based vulnerability tracking. By complementing osquery’s findings with Flan Scan’s network scans we are working towards comprehensive visibility of the services running at our edge and their vulnerabilities,” Cloudflare says.

Flan Scan first runs an Nmap scan with service detection: ICMP ping scan (IP addresses that are online), SYN scan (the 1,000 most common ports of the responding IP addresses), and service detection scan (for services running on open ports Nmap performs TCP handshake and banner grabbing scans).

Users can also conduct UDP and IPv6 scanning, and they can use any other extended feature of Nmap.

The "vulners" script tag is also present in Flan Scan’s default Nmap command, to output a list of vulnerabilities applicable to the services detected — it makes API calls to a service run by for that.

Using LaTeX, Flan Scan next converts Nmap’s output to actionable reports. The results are structured around services: vulnerable services are enumerated, each with a list of relevant vulnerabilities and the IP addresses running the service.

“Cloudflare’s mission is to help build a better Internet for everyone, not just Internet giants who can afford to buy expensive tools. We’re open sourcing Flan Scan because we believe it shouldn’t cost tons of money to have strong network security,” the security firm concludes.

Related: Free Cloudflare Tool Helps CAs Securely Issue Certificates

Related: Cloudflare Raises $150 Million

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