Vendor  : phpBB Group
URL     : http://www.phpbb.com
Version : phpBB 2.0.7a && Earlier
Risk    : Multiple Vulnerabilities



Description:
phpBB is a high powered, fully scalable, and highly customisable 
open-source bulletin board package. phpBB has a user-friendly 
interface, simple and straight forward administration panel, 
and helpful FAQ. Based on the powerful PHP server language and 
your choice of MySQL, MS-SQL, PostgreSQL or Access/ODBC database 
servers, phpBB is the ideal free community solution for all web 
sites.



Problem:
Just a few days ago I was visiting Security Focus and I saw the 
following issue.

http://www.securityfocus.com/bid/9896

I was at first thinking "Well, if you can't trust your admins 
that is as big of a security risk as any SQL Injection" After 
talking to a few people about this Irealized that a number of 
phpBB installations are run on shared hosting setups, and 
because of that this issue could be a legitimate risk. For 
example

admin_words.php?mode=edit&id=99 UNION SELECT 0,username,
user_password FROM othersite_phpbb_users WHERE user_id=2

I decided to look into this a little more and noticed similar 
issues in two other files as well. The files I found to also 
be vulnerable were "admin_smilies.php" and "admin_styles.php" 
which can also be used to query arbitrary information.

admin_smilies.php?mode=edit&id=99 UNION SELECT 0,username,0,
user_password FROM othersite_phpbb_users WHERE user_id=2

I also played around with ideas on how a malicious user could 
use this for any kind of mischief. Remember that these SQL 
issues can also be used to probably drop tables and the like 
on non phpBB installations depending on DB privledges. Below 
are the findings of my weekend off from work. :P



SQL Injection Vulnerability:
Altering queries is possible via two different files in phpBB 
2.0.7a and earlier. The affected files are "admin_smilies.php" 
and "admin_styles.php" Below is what you will see if you take 
a look at the "admin_smilies.php" file.


-----[ Start Vuln Code ] ------------------------------------

$sql = "SELECT *
  FROM " . SMILIES_TABLE . "
  WHERE smilies_id = " . $smiley_id;
$result = $db->sql_query($sql);

-----[ Ends Vulns Code ] ------------------------------------


Both of these files could also be used to conduct cross site 
scripting attacks if a logged in admin views a malicious link 
sent by an attacker. Below are examples.

admin_smilies.php?mode=edit&id=[SQL]
admin_smilies.php?mode=delete&id=[SQL]
admin_smilies.php?mode=edit&id=[XSS]
admin_smilies.php?mode=delete&id=[XSS]
admin_styles.php?mode=edit&style_id=[SQL]
admin_styles.php?mode=delete&style_id=[SQL]
admin_styles.php?mode=edit&style_id=[XSS]
admin_styles.php?mode=delete&style_id=[XSS]

Maybe an attacker could send a logged in admin a link that 
causes certain contents of the database to be dumped into a 
text file in the httpd directory for retrieval, or maybe an 
attacker can send a logged in admin a link with some script 
embedded and attempt to steal information from a cookie? All 
of those may be likely, but what I am going to talk about 
next makes it a whole lot easier for an attacker.



Command Execution Vulnerability:
While playing around I noticed it was very easy to have 
commands that were called via the GET method executed. This 
could also be very useful for an attacker if he or she were 
to combine the above issues with the one I am talking about 
right now. To make things a little clearer go into your phpBB 
admin panel and lets create a harmless test to see how this 
works. We will use the word censor feature for this example 
since it is harmless enough, but you could just as easily use 
one of the vulnerabilities found by me and explained earlier 
in this paper. Go to the page in your phpBB admin panel titled 
"Word Censors" aka "admin_words.php" Now make a word censor, 
can be anything. After it is done get the link to delete the 
word censor you just made. For example see below what the link 
looks like.

admin_words.php?mode=delete&id=1&sid=[SID]

The sid variable doesn't have to be there, and if it does then 
that particular file is probably not vuln. Now we go into our 
user level account and make a post with an image that has a link 
to the vuln command. Now when an admin views this bogus image the 
command is executed. For example take the following post contents.

[img]http://host/login.php?logout=true[/img]

A post with this in it will log out whoever views it. Imagine how 
annoying it would be for a user to have something like that in 
their signature. It would log out everyone who viewed their post(s). 
This can be used with other files as well, not just the 
"admin_styles.php", "admin_smilies.php", and "admin_words.php" 
My weekend is almost over though :-\ So I do not have much more 
time to play around with this. But remember, this works on users 
too, not just admins and mods. The only limits I have found really 
is it only works on actions that get the values of it's variables 
from the GET method and not the $HTTP_POST_VARS[] method, and do 
not check for valid session id's this includes deleting posts, 
themes, smileys, word censors and more. This kind of activity could 
also be used in signatures, pm's and the like too. Some files such 
as modcp.php seem to handle sessions properly though, so they are 
not vulnerable. This is the code that checks for valid session ID's 
If it is not present it is possibly a vulnerable file.

// session id check
if ($sid == '' || $sid != $userdata['session_id'])
{
  message_die(GENERAL_ERROR, 'Invalid_session');
}

A quick grep of the phpBB2 directory will turn up lots of results. 
You can do that to see which files are potentially vulnerable to 
this issue. Some pretty nasty stuff can come from these issues 
though. For example, if magic_quotes_gpc is off an attacker can 
make an image to exploit one of the earlier mentioned SQL 
vulnerabilities and cause the admin hash to be dumped into a text 
file for later retrieval.

admin_smilies.php?mode=edit&id=99 UNION SELECT 0,username,0,
user_password FROM phpbb_users WHERE user_id=2 INTO OUTFILE 
'/www/full/path/out.txt' 

And also in the same post have another "image" that deletes 
the post as soon as it is viewed so there is no evidence left 
behind except the text file in the httpd directory.



Solution:
I have corresponded wih the developers about these issues, and 
you can read that correspondance at the following url.

http://www.gulftech.org/vuln/phpBBEmail.txt

I think the session cheacks are definately a potential danger, 
but I have fixed the vulnerable admin files, and they can be 
downloaded at the link below. If you find any problems with the 
fixes please let me know.

http://www.gulftech.org/vuln/phpBBadminFix.rar

I will post any updated correspondance in the previously mentioned 
file, so if you would like to keep up on any progress made check 
there. The original advisory for this report can be found at the
following url @ http://www.gulftech.org/03202004.php



Credits:
Credits go to JeiAr of the GulfTech Security Research Team. 
http://www.gulftech.org