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CGI Driven Password Changes

From Terry Singleton on Sat, 05 Dec 1998

Hi there,

We recently installed a LINUX box that runs sendmail 8.9.1, we need someway for a user to be able to change their own password, most ISP's have a html form that allows them to do this.

I know this can be done with CGI and Perl, question is does anyone have anything or know of anywhere I can find something that will do the trick..

I just bought a perl/cgi so I am working in that direction, we need something asap though. I would even pay for something.

Regards,
Terry Singleton
Network Analyst

I once wrote a prototype for such a CGI script. It wasn't fancy but it used the following basic method:

The form has the following fields:

userid (login name):
current/old password:
(repeated):
new password:
(repeasted):

... and the script does the following:

• Check the consistency between the current password and the repeat (and issue a retry screen if that fails).
• start an expect (or Perl comm.pl) script that:
  • telnet to localhost
  • waits for a "login:" prompt
  • sends the userid
  • waits for a "password:" prompt
  • send the current password
  • waits for one of:
    • a shell prompt (sends passwd command)
    • the passwd prompt (if the user shell is set to /usr/bin/passwd).
    • a "login incorrect" message (aborts and returns HTML error form).
• if the process gets to .../bin/passwd's prompt:
  • send the old password
  • wait for new password prompt
  • send the new password
  • wait for repeat prompt
  • sent the new password again
  • wait for O.K. message
  • returns HTML success page.

So mostly it's a matter of writing the expect or comm.pl script.

Unfortunately I don't have the real script handy. It looked something like:

#!/usr/bin/expect -f
## by Jim Dennis ()
## This should check a username/password
## pair by opening a telnet to localhost
## and trying to use that to login
## -- you might have to adjust the last
## expect block to account for your
## system shell prompts, and error messsages

## It returns 0 on success and various non-zero
## values for various modes of failure

set timeout 5
log_user 0

gets stdin name
gets stdin pw

spawn "/usr/bin/telnet" "localhost"

expect {

-- "ogin: $"    { send -- "$name\r" }

timeout         { send -- "\r\r" }

eof             { exit 253  }
}


expect {

"ssword: $"     { send -- "$pw\r" }
}

expect {

"ast login: "    { exit 0   }
"(\\\$|%)"       { exit 0   }
"ogin incorrect" { exit 1   }
timeout          { exit 254 }
eof              { exit 253 }
}

... so you'd replace the "exit 0" clauses with something like the following to have it change the password instead of merely checking the password as the example above does.

set password [lindex $argv 1]
send "/bin/passwd\r"
expect "password:"
send "$password\r"
expect "password:"
send "$password\r"

... this assumes that you got to a shell prompt. If you use the old trick of setting the users' login shell to /bin/passwd then you'd add another expect close to the original script to respond to the prompt for "Old password" --- which you'd get in lieue of a shell prompt.

Obviously in that case you wouldn't be "send"-ing the /bin/passwd command to the shell prompt as I've done in the second line of this second code example.

There's a package that purports to do this at:

Linux Admin CGI Package Docu (English)

http://www.daemon.de/doc_en.html

... so you can try that.

You can also look at the Linux-admin mailing list archives where I'm sure I've seen Glynn Clements point people to some utility he wrote (I think I've seen this about a dozen times).

A quick trip to the Linux-Admin FAQ (http://www.kalug.lug.net/linux-admin-FAQ) led me to a list of list archives, which lead me to one with search features. Searching on "web password change" got me to a message that refers to:

ftp://win.co.nz/web-pwd

... I'm sure there are others out there.

Copyright © 1999, James T. Dennis
Published in The Linux Gazette Issue 36 January 1999

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