I recently read a piece by an infosec analyst who observed ebay.com doing a local port scan.
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.)
- 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)?
Other sites I checked that did NOT seem to be doing this:
- paypal.com: no
- ups.com: no
- fedex.com: no
- https://www.bankofamerica.com/: no
- twitter.com: no
- facebook.com: no
- duckduckgo: no
- authorize.net: no
- wellsfargo.com: no