When the Morris worm went around, one of the ways it got in was through sendmail, using the "DEBUG" command. Right after it happened, some wise-ass sent around an email telling everybody to edit their sendmail binary (with Emacs of course), search for "DEBUG", and replace the "D" will a NULL, thus disabling the "DEBUG" command.
What that actually did was change the "DEBUG" command into the "" command.
At the time I was running a mailing list from the University of Maryland, and often had to check Sun email addresses by telnetting to sun.com port 25, pressing return a couple of times to flush the telnet negotiation characters, then going "EXPN some-email-address".
So the day after the Morris worm, I go "telnet sun.com 25", hit return a couple of times, then "EXPN foobar", and it dumps out a huge torrent of debugging information, because I had accidentally switched it into debug mode by entering a blank line!
I reported it to [email protected], and they fixed it. But it's kinda silly that they would have applied such a ham fisted patch to their sendmail demon like that, based on an email that some dude on the internet sent around!
What that actually did was change the "DEBUG" command into the "" command.
At the time I was running a mailing list from the University of Maryland, and often had to check Sun email addresses by telnetting to sun.com port 25, pressing return a couple of times to flush the telnet negotiation characters, then going "EXPN some-email-address".
So the day after the Morris worm, I go "telnet sun.com 25", hit return a couple of times, then "EXPN foobar", and it dumps out a huge torrent of debugging information, because I had accidentally switched it into debug mode by entering a blank line!
I reported it to [email protected], and they fixed it. But it's kinda silly that they would have applied such a ham fisted patch to their sendmail demon like that, based on an email that some dude on the internet sent around!
https://www.rapid7.com/db/modules/exploit/unix/smtp/morris_s...
http://www.cs.unc.edu/~jeffay/courses/nidsS05/attacks/seely-...
https://spaf.cerias.purdue.edu/tech-reps/823.pdf