Port 3581: Ascent Capture Licensing — A Quiet Corner of the Registry

What This Port Is

Port 3581 is registered with IANA under the service name kfxaclicensing — short for Kofax Ascent Capture licensing. ¹ It was registered in August 2002 for license server communication in Ascent Capture, an enterprise document capture and scanning platform built by Kofax.

The product has changed names over the decades: Ascent Capture became Kofax Capture, and Kofax itself was acquired and rebranded as Tungsten Automation. The port registration never changed. ²

What It Does

In environments running Kofax Capture (now Tungsten Capture), the license server listens on this port to validate client connections. Scanning workstations and processing modules check in with the license server to confirm they're authorized to run. Without a successful handshake on this port, the software refuses to operate.

This is a common pattern in enterprise software from that era: dedicated licensing daemons that client machines must reach before doing anything useful.

The Registered Port Range

Port 3581 sits in the registered port range (1024–49151). These ports are:

• Not reserved for operating system use (that's the well-known range, 0–1023)
• Registered with IANA by vendors and protocol authors, but enforcement is voluntary
• Shared by thousands of applications, from major protocols to products like this one

The registered range is enormous — over 48,000 ports — and most of them are like port 3581: legitimately claimed, rarely encountered outside their specific ecosystem.

Will You See Traffic Here?

Unlikely, unless you're running Kofax or Tungsten Capture in your environment. If you do see unexpected traffic on port 3581, it's worth investigating — while IANA lists it as Ascent Capture, any software can technically bind to any port.

How to Check What's Listening

# macOS / Linux
sudo lsof -i :3581

# Linux (alternative)
sudo ss -tlnp | grep 3581

# Windows
netstat -ano | findstr :3581

If something is listening and you're not running Kofax software, identify the process ID and trace it. Unexpected open ports are worth understanding.