Browser Automatically Blocks Ports

While working on an ASP.Net project at work, I found a strange “feature” (I’m more inclined to call it an annoyance) that is built into certain browsers. It seems that Firefox and WebKit have automatic port blocking built into them for specific ports. I was specifically trying to use port 6000 (a seemingly random, easy to remember port) but couldn’t access the web server. After a little searching, I managed to find some information and thought I’d share it.

You can disable the behaviour in Mozilla by adding the config string network.security.ports.banned.override with a list of comma-separated ports you want to unblock. You can access the config section by typing about:config into your browser’s address bar.

And now, without further ado, here are the ports:

Ports blocked by default in
Mozilla
Port Service
1 tcpmux
7 echo
9 discard
11 systat
13 daytime
15 netstat
17 qotd
19 chargen
20 ftp data
21 ftp control
22 ssh
23 telnet
25 smtp
37 time
42 name
43 nicname
53 domain
77 priv-rjs
79 finger
87 ttylink
95 supdup
101 hostriame
102 iso-tsap
103 gppitnp
104 acr-nema
109 POP2
110 POP3
111 sunrpc
113 auth
115 sftp
117 uucp-path
119 NNTP
123 NTP
135 loc-srv / epmap
139 netbios
143 IMAP2
179 BGP
389 LDAP
465 SMTP+SSL
512 print / exec
513 login
514 shell
515 printer
526 tempo
530 courier
531 chat
532 netnews
540 uucp
556 remotefs
563 NNTP+SSL
587 submission
601 syslog
636 LDAP+SSL
993 IMAP+SSL
995 POP3+SSL
2049 nfs
4045 lockd
6000 X11
Ports blocked by default in
WebKit
Port Service
1 tcpmux
7 echo
9 discard
11 systat
13 daytime
15 netstat
17 qotd
19 chargen
20 FTP-data
21 FTP-control
22 SSH
23 telnet
25 SMTP
37 time
42 name
43 nicname
53 domain
77 priv-rjs
79 finger
87 ttylink
95 supdup
101 hostriame
102 iso-tsap
103 gppitnp
104 acr-nema
109 POP2
110 POP3
111 sunrpc
113 auth
115 SFTP
117 uucp-path
119 nntp
123 NTP
135 loc-srv / epmap
139 netbios
143 IMAP2
179 BGP
389 LDAP
465 SMTP+SSL
512 print / exec
513 login
514 shell
515 printer
526 tempo
530 courier
531 Chat
532 netnews
540 UUCP
556 remotefs
563 NNTP+SSL
587 ESMTP
601 syslog-conn
636 LDAP+SSL
993 IMAP+SSL
995 POP3+SSL
2049 NFS
3659 apple-sasl / PasswordServer [Apple addition]
4045 lockd
6000 X11
6665 Alternate IRC [Apple addition]
6666 Alternate IRC [Apple addition]
6667 Standard IRC [Apple addition]
6668 Alternate IRC [Apple addition]
6669 Alternate IRC [Apple addition]

Sources:


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