Today I'm going through using OpenCV (2.1) or Blepo to create a nice and easy to use class for feature correspondence and correspondence matching.
Normal0falsefalsefalseEN-USX-NONEX-NONEBuffer overflow exploits are commonly found problems which can cause irrevocable damage to a system if taken advantage of.
The exploit taken advantage here is two-fold but wouldn’t necessarily have to be depending on how it was done.
The function return pointer, shown in hex at 0x4C and in memory at the shifted location, is overwritten to 0x004015f9 which is the location of the assembly instructions in main preceding the arc injection function. This is equivalent to the Calc.txt file used in Exploit 1, except that it overwrites the recursive local variable i to the value 1 and it overwrites the main recursive variable i to 0, shown above at 0xBC and in memory at 0x22ccec right above the command character array. Next, the assembly needs to call GetProcAddress to find the address of a function in a library, with its arguments, the library to look in, and the function to look for, pushed on the stack. With shellcode created, it is just a matter of finding a place to insert it and a function pointer to overwrite to call it. The shellcode is clearly displayed from 0x00 to 0x63 and then it is null data that doesn’t matter until the global variable FunctPtr located at 0xB0 in the hex file and 0x404168 in memory, which we overwrite to 0x404108. SURF stances for Speeded up Robust Features and is an improvement to SIFT (Scale Invariant Feature Transform). The only way to prevent them is to be careful about coding practices and bounds check to make sure no kind of input, stream, file, command, encryption key, or otherwise can be used to overwrite a buffer past bounds.
First, vulnerable data would have to be overwritten in order to take advantage of the system function used in the ArcInjection function. The above hex overwrites the unimportant data with the letter A (0x41), the rest of the data is overwritten with what is already there in memory just in case it is important. To keep things simple, the previous exploit of using the Arc injection to run calc was used.


Firstly, nasm is used to compile the assembly with the –f flag into a binary file with “Bits 32” included in the assembly file. The trick, just like in the first exploit, is to get the shifting right so that the relative difference is the same and the correct data is overwritten. It isn't too bad to implement (and a good exercise) if you have the time but OpenCV has a nice version that does multiple octaves and octave layers.One of the drawbacks of the OpenCV implementation is that they do not have a good correspondence matching algorithm, which is a shame, since a decent one can be done extremely easily.
Each one has a code associated with it and is either a CEA code (hdmi_group=1) or a DMT code (hdmi_group=2). Firstly, because VulnerableCode.c brings a character into an integer array, which doesn’t allow us to overwrite ? of memory. The main function calls the ArcInjection function with the arguments of a predefined char array named command. However, this recursion function could be used to run multiple copies of shellcode since it calls itself multiple times with data in multiple places in memory. The MessageBoxA function can then be finally called with its arguments pushed onto the stack. This is important since the Windows library functions are 32 bit and therefore at 32 bit addresses. The GlobalBuf array is located at 0x404108 in memory, which is conveniently just before the global function pointer variable named FunctPtr, which is located at 0x404168. The code I have was written courtesy of Brian Peasley, which I have edited heavily (much to his probable dismay). Secondly, because VulnerableCode_2.c doesn’t flip all the memory into little endian form (which is good for Shellcode but makes typing words awkward).
The key points of the hex above are the ESP which starts at 0x48, the function return value at 0x4C, and the command string at 0xA0.


In order to create shellcode, the program nasm (included at the link at the top as well) was downloaded to compile assembly in to a small binary format.
At this point, the code is finished, so it calls ExitProcess from kernel32.dll with an argument of 0.
These important parts are overwritten in the memory by being shifted the correct amount from where the buffer starts, hence the large amount of arbitrary As. This is done to prevent the code from seg-faulting and make it look like the vulnerable code ended correctly even though it was exploited.
Nextly, the locations of the Windows functions displayed are different per operating system and service pack in order to prevent exploits.
The first shellcode created generates a messagebox using the Windows user32.dll library and its assembly instructions are shown in Appendix B.
Note that this is not a necessary class and can be done with a series of functions instead. The function called is MessageBoxA, which is included in the Windows user32.dll library, which is not necessarily included in the vulnerable code. However, since I use a very large library, it is often more convenient for me to group these within classes. This concludes the creation of the shellcode; however, a shortened version of the assembly is included in the link at top.



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