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masscan

Asynchronous TCP port scanner for large ranges

Internet-scale port scanner that sends SYN packets asynchronously with its own TCP/IP stack, designed to scan very large address ranges quickly.

Open sourceAGPL-3.0-only
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Homepage of masscan
Official repository page, captured by ThreatWire.

What masscan does

masscan uses its own user-mode TCP/IP stack and transmits packets asynchronously, which lets it scan very large IP ranges far faster than traditional scanners. Its command-line options are deliberately close to Nmap's.

It is used for attack surface measurement and research scanning. Fast scanning of networks you do not own can breach acceptable-use policies and laws; rate limits and exclusion lists should always be set.

Key features

  • Asynchronous transmission with a custom TCP/IP stack
  • Nmap-like command-line options
  • Banner grabbing for common protocols
  • Rate control and exclusion lists
  • XML, JSON, grepable and binary output

Licence

AGPL-3.0-only · GNU AGPL v3 · Open source

Checked by ThreatWire against the repository's licence file on 2026-10-20. GitHub detects: AGPL-3.0.

Security of masscan itself

No published advisory found for masscan in GitHub repository advisories. That does not mean the tool has no vulnerabilities.

Sources: GitHub repository advisories · checked 2026-10-20.

Categories and tags

Network scanning and analysisOSINT and attack surface discovery#port-scanner#asynchronous#c#cli

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