Websites Conducting Port Scans

Security researcher Charlie Belmer is reporting that commercial websites such as eBay are conducting port scans of their visitors.

Looking at the list of ports they are scanning, they are looking for VNC services being run on the host, which is the same thing that was reported for bank sites. I marked out the ports and what they are known for (with a few blanks for ones I am unfamiliar with):

  • 5900: VNC
  • 5901: VNC port 2
  • 5902: VNC port 3
  • 5903: VNC port 4
  • 5279:
  • 3389: Windows remote desktop / RDP
  • 5931: Ammy Admin remote desktop
  • 5939:
  • 5944:
  • 5950: WinVNC
  • 6039: X window system
  • 6040: X window system
  • 63333: TrippLite power alert UPS
  • 7070: RealAudio

No one seems to know why:

I could not believe my eyes, but it was quickly reproduced by me (see below for my observation).

I surfed around to several sites, and found one more that does this (the citibank site, see below for my observation)

I further see, at least across ebay.com and citibank.com the same ports, in the same sequence getting scanned. That implies there may be a library in use across both sites that is doing this. (I have not debugged into the matter so far.)

The questions:

  • Is this port scanning “a thing” built into some standard fingerprinting or security library? (if so, which?)
  • Is there a plugin for firefox that can block such behavior? (or can such blocking be added to an existing plugin)?

I’m curious, too.


*** This is a Security Bloggers Network syndicated blog from Schneier on Security authored by Bruce Schneier. Read the original post at: https://www.schneier.com/blog/archives/2020/05/websites_conduc.html