Information Security Internet, Intranet, Extranet Prof. dr. P.M.E. De Bra Department of Computing Science Eindhoven University of Technology Parts / Topics / Issues Basics of Internet technology / Organization Principles of Firewalls / Virtual Private Networks.
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Information SecurityInternet, Intranet, Extranet
Prof. dr. P.M.E. De Bra
Department of Computing Science
Eindhoven University of Technology
Internet standards are defined in RFCs.
Informal definition of Internet is rfc 1462:
We look at 1) TCP, 2) IP, 3) UDP and ICMP,
4) Application-level protocols, 5) Ethernet
Example: Mail dialog between client and server
svis01: 220 svis01.win.tue.nl ESMTP Sendmail 8.8.7/1.45 ready at Fri, 5 Feb 1999 23:28:31 +0100 (MET)
wwwis: HELO wwwis.win.tue.nl
svis01: 250 svis01.win.tue.nl Hello wwwis [126.96.36.199], pleased to meet you
wwwis: MAIL From: email@example.com
svis01: 250 firstname.lastname@example.org... Sender ok
1xx: command received and being processed
3xx: further action is needed
4xx: temporary error
5xx: permanent error
(HTTP has some slight deviations, see later)
GET /index.html HTTP/1.0
User-Agent: Mozilla 4.5...
... other fields ...
< empty line marks end of request >
HTTP/1.0 200 OK
Date: Mon, 08 Feb 1999 20:48:51 GMT
Last-Modified: Wed, 23 Sep 1998 ...
< empty line >
< The content of the document follows>
see: RFC 2068
echo $message | sendmail $mail_to
(message and mail_to are form fields)
if the user enters into the mail_to field:
this results in the password file being sent to email@example.com
Moral: do not use environment variables (that are set through forms) without quoting and without checking them.
See also: http://www.byte.com/art/9709/sec5/sec5.htm
Nice intro to Cypherpunk and Mixmaster at: