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* Advanced Shellcoding Techniques - by *Quar *
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Introduction

This paper assumes a working knowledge of basic shellcoding techniques, and x86 assembly, I will not rehash these in this paper. I hope to teach you some of the lesser known shellcoding techniques that I have picked up, which will allow you to write smaller and better shellcodes. I do not claim to have invented any of these techniques, except for the one that uses the div instruction.

 

The multiplicity of mul

This technique was originally developed by Sorbo of darkircop.net. The mul instruction may, on the surface, seem mundane, and it's purpose obvious. However, when faced with the difficult challenge of shrinking your shellcode, it proves to be quite useful. First some background information on the mul instruction itself.

mul performs an unsigned multiply of two integers. It takes only one operand, the other is implicitly specified by the %eax register. So, a common mul instruction might look something like this:

movl $0x0a,%eax
mul $0x0a

This would multiply the value stored in %eax by the operand of mul, which in this case would be 10*10. The result is then implicitly stored in EDX:EAX. The result is stored over a span of two registers because it has the potential to be considerably larger than the previous value, possibly exceeding the capacity of a single register(this is also how floating points are stored in some cases, as an interesting sidenote).

So, now comes the ever-important question. How can we use these attributes to our advantage when writing shellcode? Well, let's think for a second, the instruction takes only one operand, therefore, since it is a very common instruction, it will generate only two bytes in our final shellcode. It multiplies whatever is passed to it by the value stored in %eax, and stores the value in both %edx and %eax, completely overwriting the contents of both registers, regardless of whether it is necessary to do so, in order to store the result of the multiplication. Let's put on our mathematician hats for a second, and consider this, what is the only possible result of a multiplication by 0? The answer, as you may have guessed, is 0. I think it's about time for some example code, so here it is:

xorl %ecx,%ecx
mul %ecx

What is this shellcode doing? Well, it 0's out the %ecx register using the xor instruction, so we now know that %ecx is 0. Then it does a mul %ecx, which as we just learned, multiplies it's operand by the value in %eax, and then proceeds to store the result of this multiplication in EDX:EAX. So, regardless of %eax's previous contents, %eax must now be 0. However that's not all, %edx is 0'd now too, because, even though no overflow occurs, it still overwrites the %edx register with the sign bit(left-most bit) of %eax. Using this technique we can zero out three registers in only three bytes, whereas by any other method(that I know of) it would have taken at least six.

The div instruction

Div is very similar to mul, in that it takes only one operand and implicitly divides the operand by the value in %eax. Also like, mul it stores the result of the divide in %eax. Again, we will require the mathematical side of our brains to figure out how we can take advantage of this instruction. But first, let's think about what is normally stored in the %eax register. The %eax register holds the return value of functions and/or syscalls. Most syscalls that are used in shellcoding will return -1(on failure) or a positive value of some kind, only rarely will they return 0(though it does occur). So, if we know that after a syscall is performed, %eax will have a non-zero value, and that the instruction divl %eax will divide %eax by itself, and then store the result in %eax, we can say that executing the divl %eax instruction after a syscall will put the value 1 into %eax. So...how is this applicable to shellcoding? Well, their is another important thing that %eax is used for, and that is to pass the specific syscall that you would like to call to int $0x80. It just so happens that the syscall that corresponds to the value 1 is exit(). Now for an example:

xorl %ebx,%ebx
mul %ebx
push %edx
pushl $0x3268732f
pushl $0x6e69622f
mov %esp, %ebx
push %edx
push %ebx
mov %esp,%ecx
movb $0xb, %al #execve() syscall, doesn't return at all unless it fails, in which case it returns -1
int $0x80

divl %eax # -1 / -1 = 1
int $0x80

Now, we have a 3 byte exit function, where as before it was 5 bytes. However, there is a catch, what if a syscall does return 0? Well in the odd situation in which that could happen, you could do many different things, like inc %eax, dec %eax, not %eax anything that will make %eax non-zero. Some people say that exit's are not important in shellcode, because your code gets executed regardless of whether or not it exits cleanly. They are right too, if you really need to save 3 bytes to fit your shellcode in somewhere, the exit() isn't worth keeping. However, when your code does finish, it will try to execute whatever was after your last instruction, which will most likely produce a SIG ILL(illegal instruction) which is a rather odd error, and will be logged by the system. So, an exit() simply adds an extra layer of stealth to your exploit, so that even if it fails or you can't wipe all the logs, at least this part of your presence will be clear.

 

Unlocking the power of leal

The leal instruction is an often neglected instruction in shellcode, even though it is quite useful. Consider this short piece of shellcode.

xorl %ecx,%ecx
leal 0x10(%ecx),%eax

This will load the value 17 into eax, and clear all of the extraneous bits of eax. This occurs because the leal instruction loads a variable of the type long into it's desitination operand. In it's normal usage, this would load the address of a variable into a register, thus creating a pointer of sorts. However, since ecx is 0'd and 0+17=17, we load the value 17 into eax instead of any kind of actual address. In a normal shellcode we would do something like this, to accomplish the same thing:

xorl %eax,%eax
movb $0x10,%eax

I can hear you saying, but that shellcode is a byte shorter than the leal one, and you're quite right. However, in a real shellcode you may already have to 0 out a register like ecx(or any other register), so the xorl instruction in the leal shellcode isn't counted. Here's an example:

xorl %eax,%eax
xorl %ebx,%ebx
movb $0x17,%al
int $0x80

xorl %ebx,%ebx
leal 0x17(%ebx),%al
int $0x80

Both of these shellcodes call setuid(0), but one does it in 7 bytes while the other does it in 8. Again, I hear you saying but that's only one byte it doesn't make that much of a difference, and you're right, here it doesn't make much of a difference(except for in shellcode-size pissing contests =p), but when applied to much larger shellcodes, which have many function calls and need to do things like this frequently, it can save quite a bit of space.

 

Conclusion

I hope you all learned something, and will go out and apply your knowledge to create smaller and better shellcodes. If you know who invented the leal technique, please tell me and I will credit him/her.

After repeated requests for beep codes i have decided to post them here maybe they could be pinned

Standard Original IBM POST Error Codes
Code Description

1 short beep System is OK
2 short beeps POST Error - error code shown on screen No beep Power supply or system board problem Continuous beep Power supply, system board, or keyboard problem Repeating short beeps Power supply or system board problem
1 long, 1 short beep System board problem
1 long, 2 short beeps Display adapter problem (MDA, CGA)
1 long, 3 short beeps Display adapter problem (EGA)
3 long beeps 3270 keyboard card
IBM POST Diagnostic Code Descriptions
Code Description
100 - 199 System Board
200 - 299 Memory
300 - 399 Keyboard
400 - 499 Monochrome Display
500 - 599 Colour/Graphics Display
600 - 699 Floppy-disk drive and/or Adapter
700 - 799 Math Coprocessor
900 - 999 Parallel Printer Port
1000 - 1099 Alternate Printer Adapter
1100 - 1299 Asynchronous Communication Device, Adapter, or Port
1300 - 1399 Game Port
1400 - 1499 Colour/Graphics Printer
1500 - 1599 Synchronous Communication Device, Adapter, or Port
1700 - 1799 Hard Drive and/or Adapter
1800 - 1899 Expansion Unit (XT)
2000 - 2199 Bisynchronous Communication Adapter
2400 - 2599 EGA system-board Video (MCA)
3000 - 3199 LAN Adapter
4800 - 4999 Internal Modem
7000 - 7099 Phoenix BIOS Chips
7300 - 7399 3.5" Disk Drive
8900 - 8999 MIDI Adapter
11200 - 11299 SCSI Adapter
21000 - 21099 SCSI Fixed Disk and Controller
21500 - 21599 SCSI CD-ROM System

AMI BIOS Beep Codes
Code Description

1 Short Beep System OK
2 Short Beeps Parity error in the first 64 KB of memory
3 Short Beeps Memory failure in the first 64 KB
4 Short Beeps Memory failure in the first 64 KB Operational of memory
or Timer 1 on the motherboard is not functioning
5 Short Beeps The CPU on the motherboard generated an error
6 Short Beeps The keyboard controller may be bad. The BIOS cannot switch to protected mode
7 Short Beeps The CPU generated an exception interrupt
8 Short Beeps The system video adapter is either missing, or its memory is faulty
9 Short Beeps The ROM checksum value does not match the value encoded in the BIOS
10 Short Beeps The shutdown register for CMOS RAM failed
11 Short Beeps The external cache is faulty
1 Long, 3 Short Beeps Memory Problems
1 Long, 8 Short Beeps Video Card Problems

Phoenix BIOS Beep Codes
Note - Phoenix BIOS emits three sets of beeps, separated by a brief pause.

Code Description
1-1-3 CMOS read/write failure
1-1-4 ROM BIOS checksum error
1-2-1 Programmable interval timer failure
1-2-2 DMA initialisation failure
1-2-3 DMA page register read/write failure
1-3-1 RAM refresh verification failure
1-3-3 First 64k RAM chip or data line failure
1-3-4 First 64k RAM odd/even logic failure
1-4-1 Address line failure first 64k RAM
1-4-2 Parity failure first 64k RAM
2-_-_ Faulty Memory
3-1-_ Faulty Motherboard
3-2-4 Keyboard controller Test failure
3-3-4 Screen initialisation failure
3-4-1 Screen retrace test failure
3-4-2 Search for video ROM in progress
4-2-1 Timer tick interrupt in progress or failure
4-2-2 Shutdown test in progress or failure
4-2-3 Gate A20 failure
4-2-4 Unexpected interrupt in protected mode
4-3-1 RAM test in progress or failure>ffffh
4-3-2 Faulty Motherboard
4-3-3 Interval timer channel 2 test or failure
4-3-4 Time of Day clock test failure
4-4-1 Serial port test or failure
4-4-2 Parallel port test or failure
4-4-3 Math coprocessor test or failure
Low 1-1-2 System Board select failure
Low 1-1-3 Extended CMOS RAM failure

The first things you need to know about using Bit Torrent: -- Bit Torrent is aimed at broadband users (or any connection better than dialup). -- Sharing is highly appreciated, and sharing is what keeps bit torrent alive. -- A bit torrent file (*.torrent) contains information about the piece structure of the download (more on this later) -- The method of downloading is not your conventional type of download. Since downloads do not come in as one big chunk, you are able to download from many people at once, increasing your download speeds. There may be 100 "pieces" to a file, or 20,000+ pieces, all depending on what you're downloading. Pieces are usually small (under 200kb) -- The speeds are based upon people sharing as they download, and seeders. Seeders are people who constantly share in order to keep torrents alive. Usually seeders are on fast connections (10mb or higher). In this tutorial, I will be describing it all using a bit torrent client called Azureus. This client is used to decode the .torrent files into a useable format to download from other peers. From here on out, I will refer to Bit Torrent as BT. Which BT client you use, is purely up to you. I have tried them all, and my personal favorite is Azureus for many reasons. A big problem with most BT clients out there, is that they are extremely CPU intensive, usually using 100% of your cpu power during the whole process. This is the number one reason I use Azureus. Another, is a recently released plug-in that enables you to browse all current files listed on suprnova.org (the #1 source for torrent downloads). Before you use the plug-in, take a look at /http://www.suprnova.org, and browse the files. Hold your mouse over the links, and you'll notice every file ends in .torrent. This is the BT file extension. Usually, .torrent files are very small, under 200kb. They contain a wealth of information about the file you want to download. A .torrent file can contain just 1 single file, or a a directory full of files and more directories. But regardless, every download is split up into hundreds or thousands of pieces. The pieces make it much easier to download at higher speeds. Back to suprnova.org. Look at the columns: Added | Name | Filesize | Seeds | DLs (and a few more which aren't very useful.) I'll break this down. Added: Self explanitory, its the date the torrent was added. Name: Also self explanitory. Filesize: Duh Seeds: This is how many people are strictly UPLOADING, or sharing. These people are the ones that keep .torrent files alive. By "alive", I mean, if there's no one sharing the .torrent file, no one can download. DLs: This is how many people currently downloading that particular torrent. They also help keep the torrent alive as they share while they download. It's always best to download using a torrent that has a decent amount of seeders and downloaders, this way you can be assured there's a good chance your download will finish. The more the better. Now that you should understand how torrent files work, and how to use them, on to Azureus! First, get JAVA! You need this to run Azureus, as java is what powers it. Get Java here: /http://java.sun.com/j2se/1.4.2/download.html Next, get Azureus at: /http://azureus.sourceforge.net Next, get the Suprnovalister plugin from /http://s93732957.onlinehome.us/storage/suprnovalister.jar Install Java JRE before you do ANYTHING. Install Azureus, and then in the installation folder, create 2 more folders. ./Plugins/suprnovalister (For example, if you installed Azureus to C:\PROGRAM FILES\AZUREUS, create C:\PROGRAM FILES\AZUREUS\PLUGINS\SUPRNOVALISTER). Next, put the suprnovalister.jar file that you downloaded, in that folder. Load up Azureus, and if you want, go through the settings and personalize it. The tab labeled "My Torrents" is the section of Azureus you need the most often. That lists all your transfers, uploads and downloads. It shows every bit of information you could possibly want to know about torrents you download. In the menu bar, go to View > Plugins > Suprnova Lister. This will open up a new tab in Azureus. Click on "Update Mirror". This will get a mirror site of suprnova.org containing all current torrent files available. Once a mirror is grabbed, choose a category from the drop-down box to the left and click "Update". Wah-lah, all the available downloads appear in the main chart above. Just double click a download you want, and bang its starting to download. Open the "My Torrents" tab again to view and make sure your download started. After your download has finished, be nice, and leave the torrent transferring. So people can get pieces of the file from you, just as you got pieces from other people. Alternatively, if you don't want to use the plugin... you can just head to suprnova.org and download files to any folder. Then go to File > Open > .torrent File in Azureus. This should about wrap it up for the Bit Torrent Tutorial. If you guys think of anything I should add, or whatnot, just let me know and I'll check into it.

Getting used to using your keyboard exclusively and leaving your mouse behind will make you much more efficient at performing any task on any Windows system. I use the following keyboard shortcuts every day:

Windows key + R = Run menu

This is usually followed by:
cmd = Command Prompt
iexplore + "web address" = Internet Explorer
compmgmt.msc = Computer Management
dhcpmgmt.msc = DHCP Management
dnsmgmt.msc = DNS Management
services.msc = Services
eventvwr = Event Viewer
dsa.msc = Active Directory Users and Computers
dssite.msc = Active Directory Sites and Services
Windows key + E = Explorer

ALT + Tab = Switch between windows

ALT, Space, X = Maximize window

CTRL + Shift + Esc = Task Manager

Windows key + Break = System properties

Windows key + F = Search

Windows key + D = Hide/Display all windows

CTRL + C = copy

CTRL + X = cut

CTRL + V = paste

Also don't forget about the "Right-click" key next to the right Windows key on your keyboard. Using the arrows and that key can get just about anything done once you've opened up any program.

Keyboard Shortcuts

[Alt] and [Esc] Switch between running applications

[Alt] and letter Select menu item by underlined letter

[Ctrl] and [Esc] Open Program Menu

[Ctrl] and [F4] Close active document or group windows (does not work with some applications)

[Alt] and [F4] Quit active application or close current window

[Alt] and [-] Open Control menu for active document

Ctrl] Lft., Rt. arrow Move cursor forward or back one word

Ctrl] Up, Down arrow Move cursor forward or back one paragraph

[F1] Open Help for active application

Windows+M Minimize all open windows

Shift+Windows+M Undo minimize all open windows

Windows+F1 Open Windows Help

Windows+Tab Cycle through the Taskbar buttons

Windows+Break Open the System Properties dialog box

 

acessability shortcuts

Right SHIFT for eight seconds........ Switch FilterKeys on and off.

Left ALT +left SHIFT +PRINT SCREEN....... Switch High Contrast on and off.

Left ALT +left SHIFT +NUM LOCK....... Switch MouseKeys on and off.

SHIFT....... five times Switch StickyKeys on and off.

NUM LOCK...... for five seconds Switch ToggleKeys on and off.

explorer shortcuts

END....... Display the bottom of the active window.

HOME....... Display the top of the active window.

NUM LOCK+ASTERISK....... on numeric keypad (*) Display all subfolders under the selected folder.

NUM LOCK+PLUS SIGN....... on numeric keypad (+) Display the contents of the selected folder.

NUM LOCK+MINUS SIGN....... on numeric keypad (-) Collapse the selected folder.

LEFT ARROW...... Collapse current selection if it's expanded, or select parent folder.

RIGHT ARROW....... Display current selection if it's collapsed, or select first subfolder.

 

Type the following commands in your Run Box (Windows Key + R) or Start Run

devmgmt.msc = Device Manager
msinfo32 = System Information
cleanmgr = Disk Cleanup
ntbackup = Backup or Restore Wizard (Windows Backup Utility)
mmc = Microsoft Management Console
excel = Microsoft Excel (If Installed)
msaccess = Microsoft Access (If Installed)
powerpnt = Microsoft PowerPoint (If Installed)
winword = Microsoft Word (If Installed)
frontpg = Microsoft FrontPage (If Installed)
notepad = Notepad
wordpad = WordPad
calc = Calculator
msmsgs = Windows Messenger
mspaint = Microsoft Paint
wmplayer = Windows Media Player
rstrui = System Restore
netscp6 = Netscape 6.x
netscp = Netscape 7.x
netscape = Netscape 4.x
waol = America Online
control = Opens the Control Panel
control printers = Opens the Printers Dialog

internetbrowser

type in u're adress "google", then press [Right CTRL] and [Enter]
add www. and .com to word and go to it

For Windows XP:

Copy. CTRL+C
Cut. CTRL+X
Paste. CTRL+V
Undo. CTRL+Z
Delete. DELETE
Delete selected item permanently without placing the item in the Recycle Bin. SHIFT+DELETE
Copy selected item. CTRL while dragging an item
Create shortcut to selected item. CTRL+SHIFT while dragging an item
Rename selected item. F2
Move the insertion point to the beginning of the next word. CTRL+RIGHT ARROW
Move the insertion point to the beginning of the previous word. CTRL+LEFT ARROW
Move the insertion point to the beginning of the next paragraph. CTRL+DOWN ARROW
Move the insertion point to the beginning of the previous paragraph. CTRL+UP ARROW
Highlight a block of text. CTRL+SHIFT with any of the arrow keys
Select more than one item in a window or on the desktop, or select text within a document. SHIFT with any of the arrow keys
Select all. CTRL+A
Search for a file or folder. F3
View properties for the selected item. ALT+ENTER
Close the active item, or quit the active program. ALT+F4
Opens the shortcut menu for the active window. ALT+SPACEBAR
Close the active document in programs that allow you to have multiple documents open simultaneously. CTRL+F4
Switch between open items. ALT+TAB
Cycle through items in the order they were opened. ALT+ESC
Cycle through screen elements in a window or on the desktop. F6
Display the Address bar list in My Computer or Windows Explorer. F4
Display the shortcut menu for the selected item. SHIFT+F10
Display the System menu for the active window. ALT+SPACEBAR
Display the Start menu. CTRL+ESC
Display the corresponding menu. ALT+Underlined letter in a menu name
Carry out the corresponding command. Underlined letter in a command name on an open menu
Activate the menu bar in the active program. F10
Open the next menu to the right, or open a submenu. RIGHT ARROW
Open the next menu to the left, or close a submenu. LEFT ARROW
Refresh the active window. F5
View the folder one level up in My Computer or Windows Explorer. BACKSPACE
Cancel the current task. ESC
SHIFT when you insert a CD into the CD-ROM drive Prevent the CD from automatically playing.

Use these keyboard shortcuts for dialog boxes:

To Press
Move forward through tabs. CTRL+TAB
Move backward through tabs. CTRL+SHIFT+TAB
Move forward through options. TAB
Move backward through options. SHIFT+TAB
Carry out the corresponding command or select the corresponding option. ALT+Underlined letter
Carry out the command for the active option or button. ENTER
Select or clear the check box if the active option is a check box. SPACEBAR
Select a button if the active option is a group of option buttons. Arrow keys
Display Help. F1
Display the items in the active list. F4
Open a folder one level up if a folder is selected in the Save As or Open dialog box. BACKSPACE

If you have a Microsoft Natural Keyboard, or any other compatible keyboard that includes the Windows logo key and the Application key , you can use these keyboard shortcuts:

Display or hide the Start menu. WIN Key
Display the System Properties dialog box. WIN Key+BREAK
Show the desktop. WIN Key+D
Minimize all windows. WIN Key+M
Restores minimized windows. WIN Key+Shift+M
Open My Computer. WIN Key+E
Search for a file or folder. WIN Key+F
Search for computers. CTRL+WIN Key+F
Display Windows Help. WIN Key+F1
Lock your computer if you are connected to a network domain, or switch users if you are not connected to a network domain. WIN Key+ L
Open the Run dialog box. WIN Key+R
Open Utility Manager. WIN Key+U

accessibility keyboard shortcuts:

Switch FilterKeys on and off. Right SHIFT for eight seconds
Switch High Contrast on and off. Left ALT+left SHIFT+PRINT SCREEN
Switch MouseKeys on and off. Left ALT +left SHIFT +NUM LOCK
Switch StickyKeys on and off. SHIFT five times
Switch ToggleKeys on and off. NUM LOCK for five seconds
Open Utility Manager. WIN Key+U

shortcuts you can use with Windows Explorer:

Display the bottom of the active window. END
Display the top of the active window. HOME
Display all subfolders under the selected folder. NUM LOCK+ASTERISK on numeric keypad (*)
Display the contents of the selected folder. NUM LOCK+PLUS SIGN on numeric keypad (+)
Collapse the selected folder. NUM LOCK+MINUS SIGN on numeric keypad (-)
Collapse current selection if it's expanded, or select parent folder. LEFT ARROW
Display current selection if it's collapsed, or select first subfolder. RIGHT ARROW