If we do info functions from gdb it will list all the functions and their memory addresses, we can also do that with objdump. Now we will use pattern_offset to know what is the location of 0圆3413163Īnd we get exact match at offset 64, This means that the buffer size is 64 chars and after that the overflow happens.įinding the memory address of the function The segfault happens and we see where it happened: 0圆3413163 We do c to make it continue then pass our argument This makes the program break after the first instruction of the function main() Now let’s run the program in gdb, I’m using gdb-peda Pattern_create creats a unique string of a defined length so we will create a pattern of 100 chars. Metasploit has two scripts called pattern_create and pattern_offset, you can find them on kali in /usr/share/metasploit-framework/tools/exploit To make things easier I compiled the program on my kali box to start testing there. The second thing is to find the memory address of the function that we need to execute. The first thing is to know where the buffer overflow happens, Because here we have given the program an argument of 100 chars but we don’t know exactly the size of the buffer. We see that the function pointer was calling the address 0x41414141 and 0x41 is the hex of “A”. That memory address is stored in a variable and we can overwrite that variable when we exceed the buffer. So now we have an idea about what’s happening here, There’s a function pointer that executes a function based on the given memory address of that function. We need to confirm that the program is vulnerable to a buffer overflow so we can pass an argument of 100 chars and see what happensĪnd we see a segfault which confirms that a buffer overflow happened, we also see this line : “calling function pointer, jumping to 0x41414141” We don’t see any output so we should give it an argument. Let’s first look at the program and see what does it do. If you haven’t read my previous articles about buffer overflow I recommend reading them first. Because in a real situation we won’t have the source of the program right ? Let’s see
#Buffer overflow 1 code#
Now with stack3 we are given the source code but We are not going to use it, Instead of that we will use some practical techniques to solve this challenge. Hey I’m back again with another article, today I’m going to solve protostar stack3 but this time it’s going to be a bit different, In the last two articles I solved stack0, stack1 and stack2 and I used the source code of the binaries to identify where the buffer overflow happens and what exploit to use. Finding the memory address of the functionīuffer Overflow Examples, Overwriting a function pointer - protostar stack3 Introduction.Buffer Overflow Examples, Overwriting a function pointer - protostar stack3.
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