Implementing Session Support: Client & Server Side Mechanisms

Implementing Session Support COEN 351

State Maintenance • Client Side Mechanisms • Cookies • Client needs to allow cookies • Cookie handling done by browser • Hidden Fields in Forms • Each page has to be rebuild to contain correct form • Fat URL • Each page has to be rebuild with correct links • Server Side Mechanisms • Files • Database • Web server • Long running process that can crash • Needs to use a client side mechanism • Security Implication: • CLIENT CAN CHANGE ALL INFORMATION

Server Side Support • Apache:Session • Perl module failed test for windows • CGI:Session • Homemade Session Support • Use to investigate security issues

Using a session database mysql> create database session; mysql> use session; mysql> create table sessionid ( -> id MEDIUMINT NOT NULL AUTO_INCREMENT, -> name CHAR(30) NOT NULL, -> PRIMARY KEY (id) -> );

Using a session database mysql> show tables; +-------------------+ | Tables_in_session | +-------------------+ | sessionid | +-------------------+ 1 row in set (0.00 sec) mysql> INSERT INTO sessionid (name) VALUES ('thomas'); Query OK, 1 row affected (0.10 sec) mysql> INSERT INTO sessionid (name) VALUES ('bob'),('jim'); Query OK, 2 rows affected (0.04 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM sessionid ORDER BY id; +----+--------+ | id | name | +----+--------+ | 1 | thomas | | 2 | bob | | 3 | jim | +----+--------+ 3 rows in set (0.00 sec)

Creating a Password Database mysql> create table user ( -> name VARCHAR(8), -> password VARCHAR(8), -> primary key (name) -> ); Query OK, 0 rows affected (0.16 sec) mysql> INSERT INTO user -> VALUES ('JoeDoe','12345'), ('JaneDoe','12345') -> ; Query OK, 2 rows affected (0.09 sec) Records: 2 Duplicates: 0 Warnings: 0

Sample Application • Login Page • Typically form that is self-referring • When user info is submitted, page acts differently • Acceptance page that creates a session • Stores session id in cookie

Login Page #!/perl/bin/perl.exe use strict; use CGI qw/:standard/; use MIME::Base64::URLSafe; #I had problems with this module under build 819 my $q = new CGI; print $q->header(-type => "text/html"); print $q->start_html("Santa Claus University Login Page"); print $q->h1("Welcome to Santa Claus University"); print $q->start_form( -action => "session1.cgi", -method => 'GET'), $q->p("Please enter your account"), $q->textfield (-name => "name"), $q->p("Please enter your password"), $q->textfield (-name => "pwd"), $q->p(" "), $q->submit (-name => 'choice', -value => "Submit" ), $q->end_form(); print $q->end_html; More normal: -action => url()

Login Page <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-US"> <head> <title>Santa Claus University Login Page</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> </head> <body> <h1>Welcome to Santa Claus University</h1><form method="get" action="session1.cgi" enctype="multipart/form-data"> <p>Please enter your account</p><input type="text" name="name" value="thomas" /><p>Please enter your password</p><input type="text" name="pwd" value="hallo" /><p> </p><input type="submit" name="choice" value="Submit" /></form> </body> </html> Notice that there is currently no protection for the data to be transmitted.

Creating a Session #!/perl/bin/perl.exe use strict; use DBI; use CGI qw/:standard :html3/; use CGI::Carp qw/ fatalsToBrowser/; #for debugging only use MIME::Base64::URLSafe; #I had problems with this module under build 819 my $q = new CGI; #Get information from GET data: my $username = param('name'); my $pwd = param('pwd');

Creating a Session my $dbh = DBI->connect ("DBI:mysql:host=localhost;database=session", "root", "none",{PrintError => 0, RaiseError => 1} ); my $sth = $dbh->prepare("SELECT * FROM user WHERE name = '$username' and password = '$pwd' "); $sth->execute(); my $ref = $sth->fetchrow_hashref (); $sth->finish(); if (!defined($ref)) { print "Location: http://192.168.0.13/cgi-bin/session.cgi\n\n" } else { code on next page } Possibility of SQL injection attack! Would it be better to check results?

Creating a Session else { #create entry in sessionid, get session ID, and clean up table $dbh->do ("INSERT INTO sessionID (id,name) VALUES(NULL,'$username')" ); my $ref = $dbh->selectcol_arrayref("SELECT LAST_INSERT_ID()"); my $sessionid = @{$ref}[0]; $dbh->do("DELETE LOW_PRIORITY FROM sessionid WHERE id < '$sessionid' and name = '$username'"); mysql> select * from sessionid; +----+---------+ | id | name | +----+---------+ | 41 | JoeDoe | | 42 | JaneDoe | +----+---------+ 2 rows in set (0.05 sec) Clean up session table Is this code vulnerable to a race condition?

Creating a Session else { … my $cookievalue1 = urlsafe_b64encode($sessionid); my $cookievalue2 = urlsafe_b64encode($username); my $cookie1 = $q->cookie ( -name => 'sessionID', -value => $cookievalue1, -expires => "+1d" ); my $cookie2 = $q->cookie ( -name => 'account', -value => $cookievalue2, -expires => "+1d" ); print $q->header(-type => "text/html", -cookie => [$cookie1,$cookie2]); print $q->start_html("Santa Claus University Login Page"); print $q->h1("Welcome to Santa Claus University"); print $q->start_form( -action => "session2.cgi", -method => 'GET'), $q->hidden($cookievalue1), $q->submit (-name => 'Continue', -value => "Submit" ), $q->end_form(); print $q->end_html; } Cookie values are not protected!

Maintaining Session Data use strict; use DBI; use CGI qw/:standard :html3/; use CGI::Carp qw/ fatalsToBrowser/; use MIME::Base64::URLSafe; my $q = new CGI; print $q->header(-type => "text/html"); print $q->start_html("Santa Claus University Login Page"), $q->h1("Welcome to Santa Claus University"), $q->p("We offer degrees for money."); foreach my $name ($q->cookie()) { my $value = urlsafe_b64decode($q->cookie($name)); print $q->p("$value"); } print $q->end_html; No authentication of cookie values.

Security Problems • We need to use cookies / fat URLs to refer to the current session name. • This information needs to be protected • against alteration • against substitution

Implementing Session Support: Client & Server Side Mechanisms