![]() ![]() ASLR randomizes the bases address of loaded applications and DLLs every time the operation system is booted.ĭata Execution Prevention (DEP) prevents certain memory sectors, e.g. It does this by randomly offsetting the location of modules and certain in-memory structures. Address Space Layout Randomization (ASLR) is a technology used to help prevent shellcode from being successful. Other, more advanced mitigation techniques for buffer overflow attacks include ASLR and DEP. ![]() This blog won’t go into the different nuances between the two functions. An alternative option could be to use a function called ‘strncpy’, which is considered by some to be a safer option because you must also pass the maximum length the destination buffer can accept (albiet strncpy has its own shortcomings). In the code used in Figure 1, a different function could have been used instead of strcpy, which is considered insecure. Checks should be done to make sure input matches the acceptable length, type, and content that is expected by the program. Input validation is performed to ensure only properly formed data is entering the workflow of an information system. This buffer overflow attack could have been prevented by using input validation. For example, the attacker could point the instruction pointer to an area in memory containing malicious shellcode, thus giving the attacker control of the victim’s machine, which we will cover in a later series on this topic. Therefore, the program doesn’t know what to do next and crashes.Īnother option for an attacker would be to overwrite the instruction pointer with an address in memory the attacker has write access to, therefore controlling what the program does next. Therefore, the instruction pointer is looking in the memory address “\x41\x41\x41\x41”, which is either empty or contains random junk. The return address is now full of A’s or “\x41”, which is the hexadecimal representation of the letter A. The return address will become the EIP when the function returns. The remaining A’s have overflowed the buffer and have filled the return address. ![]() The reason the program crashed is because the buffer array was only meant to hold ten characters. Figure 4 – Overflowing the buffer and causing the program to crash. ![]()
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