Peter Van Eeckhoutte's Blog

Archive for the ‘Exploit Writing Tutorials’ Category

A few moments ago I published a detailed write-up, explaining the steps I took to build a 0day exploit for a zip file handling bug in QuickZip, on the Offensive Security blog. You can read the article here : http://www.offensive-security.com/blog/vulndev/quickzip-stack-bof-0day-a-box-of-chocolates/ Read more »

Over the last couple of months, I have written a set of tutorials about building exploits that target the Windows stack. One of the primary goals of anyone writing an exploit is to modify the normal execution flow of the application and trigger the application to run arbitrary code… code that is injected by the attacker and that could allow the attacker to take control of the computer running the application. This type of code is often called “shellcode”, because one of the most used targets of running arbitrary code is to allow an attacker to get access to a remote shell / command prompt on the host, which will allow him/her to take further control of the host.  While this type of shellcode is still used in a lot of cases, tools such as Metasploit have …

When I started Win32 exploit development many years ago, my preferred debugger at the time was WinDbg (and some Olly). While Windbg is a great and fast debugger, I quickly figured out that some additional/external tools were required to improve my exploit development experience. Despite the fact that the command line oriented approach in windbg has many advantages, it appeared not the best tool to search for good jump addresses, or to list non-safeseh compiled / non-aslr aware modules, etc….  Ok, looking for a simple “jmp esp” is trivial, but what if you are looking for all pop pop ret combinations in non-safeseh compiled modules…   Not an easy task. It is perfectly possible to build plugins for Windbg, but the ones that I have found (MSEC, byakugan (Metasploit)) don’t always work the way I want them …

Introduction Easter is still far away, so this is probably the right time to talk about ways to hunting for eggs (so you would be prepared when the easter bunny brings you another 0day vulnerability) In the first parts of this exploit writing tutorial series, we have talked about stack based overflows and how they can lead to arbitrary code execution. In all of the exploits that we have built so far, the location of where the shellcode is placed is more or less static and/or could be referenced by using a register (instead of a hardcoded stack address), taking care of stability and reliability. In some parts of the series, I have talked about various techniques to jump to shellcode, including techniques that would use one or more trampolines to get to the shellcode.  In …

Finally … after spending a couple of weeks working on unicode and unicode exploits, I’m glad and happy to be able to release this next article in my basic exploit writing series : writing exploits for stack based unicode buffer overflows (wow – that’s a mouthful). You may (or may not) have encountered a situation where you’ve performed a stack buffer overflow, overwriting either a RET address or a SEH  record, but instead of seeing 0×41414141 in EIP, you got 0×00410041. Sometimes, when data is used in a function, some manipulations are applied. Sometimes data is converted to uppercase, to lowercase, etc…  In some situations data gets converted to unicode.  When you see 0×00410041 in EIP, in a lot of cases, this probably means that your payload had been converted to unicode before it was put on the …

Introduction In all previous tutorials in this Exploit writing tutorial series, we have looked at building exploits that would work on Windows XP / 2003 server. The success of all of these exploits (whether they are based on direct ret overwrite or exception handler structure overwrites) are based on the fact that a reliable return address or pop/pop/ret address must be found, making the application jump to your shellcode. In all of these cases, we were able to find a more or less reliable address in one of the OS dll’s or application dll’s. Even after a reboot, this address stays the same, making the exploit work reliably. Fortunately for the zillions Windows end-users out there, a number of protection mechanisms have been built-in into the Windows Operating systems. – Stack cookies (/GS Switch cookie) …

In the first parts of this exploit writing tutorial, I have mainly used Windbg as a tool to watch registers and stack contents while evaluating crashes and building exploits. Today, I will discuss some other debuggers and debugger plugins that will help you speed up this process. A typical exploit writing toolkit arsenal should at least contain the following tools : windbg (for a list of Windbg commands, click here) ollydbg immunity debugger (requires python) metasploit pyDbg (if you are using python and want to build your own custom debugger, as explained in the awesome Gray Hay Python book scripting tools …