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So Telnet as a client is not dead though, right? A long time ago, I used to use the Telnet client to talk to SMTP servers (on port 25) and send spoofed emails t
by AnonHP 8mo ago
So Telnet as a client is not dead though, right? A long time ago, I used to use the Telnet client to talk to SMTP servers (on port 25) and send spoofed emails to friends for fun.
With port blocking widening in scope, I’ve long believed that we would one day have every service and protocol listening on port 443. Since all other ports are being knocked off in the name of security, we’ll end up having one port that makes port based filtering useless.
- ajross 8mo agoNone of this affects the use of telnet the client program nor the ability to run a telnetd on your own host (but do be sure it's patched!). What's happened is that global routing on the internet (or big chunks of it, it's not really clear) has started blocking telnet's default port to protect presumably-unpatched/unpatchable dinosaur systems from automated attack. So you can no longer (probably) rely on getting to a SMTP server to deliver that spoofed email unless you can do it from its own local environment.
- pkaeding 8mo agoYou would still be able to use the telnet client to connect to an SMTP server on TCP port 25, just not port 23, right? I don't think that part changed here.
- emmelaich 8mo ago> started blocking telnet's default port But that's 23 and smtp is 25.
- jonprobably 8mo agoSMTP has and is almost blocked everywhere to dissuade spam.
- dwedge 8mo agoPresumably not on the SMTP servers they were connecting to. There are millions of IPs with port 25 open, without them email wouldn't work, so I'm not sure what you mean
- einr 8mo agoThey probably mean that port 25 is blocked on consumer ISPs/residential IP blocks to prevent malware from running an smtpd on an infected home computer or router (which used to happen a lot), but on a higher level of course no one blocks SMTP.
- mmh0000 8mo agonetcat, socat and openssl s_client are all available for general manual connection testing. As are many other tools. But the ones above are basically far better direct telnet alternatives.
- EE84M3i 8mo agoI've never really understood why it's a thing to use a telnet client for transmitting text on a socket for purposes other than telnet. My understanding is that telnet is a proper protocol with escape sequences/etc, and even that HTTP/SMTP/etc require things like \r\n for line breaks. Are these protocols just... close enough that it's not a problem in practice for text data?
- swinglock 8mo agoBecause it's there.
- deleted 8mo ago[deleted]
- prmoustache 8mo agoIt hasn't for the most part of the last 2 decades.
- 1718627440 8mo agoThe telnet client comes with MS Windows, Linux and macOS. The only platforms were you need to install some extra component are Android and iOS.
- prmoustache 8mo agoMany companies have been preventing its execution or removing the package by default for a number of years. Also most linux containers do not ships with such binaries to save on img size and reduce vuln management overhead.
- dudefeliciano 8mo agoI don’t remember how I did it but when I was about 12 years old I somehow managed to send SMS from Telnet to cell phones, and to the receiver they appeared to be sent by an official Telecom account - good that I was still an innocent child, had I discovered this a few years later I may have tried doing something nefarious with it.