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

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