4 ms·

None 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

by ajross 9mo ago

None 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 9mo ago
You 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.
- ajross 9mo ago
  It's... not super clear from the article whether this is a port block or a stateful protocol thing. But yes, you're probably right and SMTP spoofing is probably safe for now.
  - Balinares 9mo ago
    I read it as a clear port 23 block.
emmelaich 9mo ago
> started blocking telnet's default port But that's 23 and smtp is 25.
- jonprobably 9mo ago
  SMTP has and is almost blocked everywhere to dissuade spam.
  - dwedge 9mo ago
    Presumably 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 9mo ago
      They 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.