rxgoogle.cgi XSS Vulnerability.

[Shaun Colley <shaunige () yahoo co uk>]

Introduction
############

rxgoogle.cgi is..."Provide your website visitors with
your own net search program. This script allows your
visitor to perform web search within your site without
redirecting. You can set up RxGoogle search engine in
just minutes and it's FREE!".

rxgoogle.cgi is vulnerable to a simple XSS attack,
potentially allowing an attacker to steal a users
authentication cookie for that site (if there is one),
or insert other malicious code into a search query and
trick a legimate user into visiting the URL.

Although rxgoogle.cgi is a new CGI script, and the bug
is low risk, I considered this worth posting because a
lot of people like to keep an up to date record of ALL
CGI scripts known to be insecure in some way or
another.


The bug
#######

The bug exists due to very bad user-input
sanitization, hence a failure to filter bad characters
such as metacharacters.  

PoC:

http://host.com/cgi-bin/rxgoogle.cgi?query=%3Cscript%3Ealert%28%22XSS%22%29%3C%2Fscript%3E



The fix
#######

I have written a patch to fix the vulnerability.


----START
--- rxgoogle.cgi        2004-02-04 14:20:38.000000000 -0500
+++ test        2004-02-04 14:27:29.000000000 -0500
@@ -197,7 +197,13 @@
 my $req = new HTTP::Request GET => "$url";
 my $res = $ua->request($req);
 if ($res->is_success) { $page_returned =
$res->content; }   return $page_returned;}
-sub parse{my (@pairs, %in);my (@pairs, %in);my
($buffer, $pair, $name, $value);if
($ENV{'REQUEST_METHOD'} eq 'GET') {@pairs = split(/&/,
$ENV{'QUERY_STRING'});}elsif($ENV{'REQUEST_METHOD'} eq
'POST') {read(STDIN, $buffer,
$ENV{'CONTENT_LENGTH'});@pairs = split(/&/,
$buffer);}PAIR: foreach $pair (@pairs) {($name,
$value) = split(/=/, $pair);$name =~ tr/+/ /;$name =~
s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",
hex($1))/eg;$value =~ tr/+/ /;$value =~
s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",
hex($1))/eg;($value eq "---") and next PAIR;exists
$in{$name} ? ($in{$name} .= "~~$value") : ($in{$name} 
= $value);}return %in;}
+
+# This parsing routine poorly sanitized user-input,
thus allowing injection
+# of metametachars, such as '<' and '>'.  I have
patched the problem now, by
+# filtering input quite well now.
+#
+# -Shaun2k2
+sub parse{$OK_CHARS='-a-zA-Z0-9_.@'; my (@pairs,
%in);my (@pairs, %in);my ($buffer, $pair, $name,
$value);if ($ENV{'REQUEST_METHOD'} eq 'GET') {@pairs =
split(/&/,
$ENV{'QUERY_STRING'});}elsif($ENV{'REQUEST_METHOD'} eq
'POST') {read(STDIN, $buffer,
$ENV{'CONTENT_LENGTH'});@pairs = split(/&/,
$buffer);}PAIR: foreach $pair (@pairs) {($name,
$value) = split(/=/, $pair);$name =~ tr/+/ /;$name =~
s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",
hex($1))/eg;$name =~ s/[^$OK_CHARS]/_/go;$value =~
tr/+/ /;$value =~
s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",
hex($1))/eg;$value =~ s/[^$OK_CHARS]/_/go;($value eq
"---") and next PAIR;exists $in{$name} ? ($in{$name}
.= "~~$value") : ($in{$name}  = $value);}return %in;}
 sub html_navbar{my
($maxhits,$current,$numhits,$url)=0;my ($html, $nh,
$prev_hit, $next_hit, $left, $right, $first, $last,
$lower, $upper)="";$maxhits  =shift; $numhits  =shift;
$current  =shift; $url      =shift;
$nh=int($current/$maxhits)+1;  $prev_hit=$nh-1;         
$next_hit=$nh+1;                if (($current + $maxhits) >=
$numhits) {$next_hit=0;}if ($numhits > $maxhits) {    
     $left  = $nh; $right = int($numhits/$maxhits) -
$nh;                ($left > 7)  ? ($lower = $left -
7) : ($lower = 1);        ($right > 7) ? ($upper = $nh
+ 7)   : ($upper = int($numhits/$maxhits) + 1);       
(7 - $nh >= 0) and ($upper = $upper + (8 - $nh));     
  ($nh > ($numhits/$maxhits - 7)) and ($lower = $lower
- ($nh - int($numhits/$maxhits - 7) - 1));       
$html = "";        ($nh > 1) and ($html .= qq~<a
href="$url&start=$prev_hit">[previous]</a> ~);       
for ($i = 1; $i <= int($numhits/$maxhits) + 1; $i++) {
           if ($i < $lower) { $html .= " ... "; $i =
($lower-1); next; }                       if ($i >
$upper) { $html .= " ... "; last; }            ($i ==
$nh) ?                ($html .= qq~$i ~) :            
   ($html .= qq~<a href="$url&start=$i">$i</a> ~);    
       (($i * $maxhits) >= $numhits) and last;      
}if ($next_hit) {        $html .= qq~<a
href="$url&start=$next_hit">[next]</a> ~ unless ($nh
== $i);         }            }return $html;}    
 
 1;
@@ -224,4 +230,4 @@
    print WRITEIT "$site\n";
    close(WRITEIT);
 }
-        
\ No newline at end of file
+        
---END


Apply the patch as below:

$ patch rxgoogle.cgi rxgoogle-xss.patch


The bug is now fixed, due to proper sanitization now
taking place. 


Credit
######

This vulnerability was discovered by shaun2k2 / Shaun
Colley.  The patch was written by shaun2k2 / Shaun
Colley.




Thank you for your time.
Shaun.


        
        
                
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