Ports that are blocked by browsers (2023)
8 comments
·May 13, 2025joecool1029
banana_giraffe
Interestingly, they are there:
https://github.com/mozilla/gecko-dev/blob/771bc161e016e2bd1f...
(Confirmed on a recent-ish Firefox browser)
They look to have been there for at least 5 years, dunno when they were added before that.
wayvey
Wow, been a full stack webdev for over a decade and somehow I don't remember ever encountering this. Nice post!
Dwedit
If you really really need to connect to a server running on a "forbidden port", you can use client-side network forwarding, such as SSH tunnels or Netcat.
snvzz
A glaring omission is listing ports for any browser other than firefox.
Do they do the same? Are they the same ports?
banana_giraffe
Different ports, here's the list for Chromium:
https://github.com/chromium/chromium/blob/76892135714e5b4f16...
rolph
ports have standardized default usages, this means new or poorly configured installs are prone to abuse, so its generally good to limit these ports in some way.
https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbe...
null
I'm surprised IRC wasn't on the list after the IRC flooding incident years ago: https://news.softpedia.com/news/Firefox-Bug-Used-to-Harass-a...
I guess the concern is targeting local services not remote ones.