Exploit exercises - Protostar - Net 3

Last network level is a bit more challenging. There are a couple of traps here. The idea of the program is like that: it reads length(16-bit) of the future input, then reads that amount of bytes. First byte of the input should have the value of 23 to proceed to login function. Buffer with input data is used as an argument to the login function.

Exploit exercises - Protostar - Net 2

Third network level requires to sum 4 integers and send result. They are provided by the server. Nothing special just use of pack and unpack methods.

Exploit exercises - Protostar - Net 1

Next level requires to convert binary integer to its string representation. All we have to do is read 4 bytes, convert bytes to int then convert it into string. Ruby have unpack method of String class to do required transformation.

Exploit exercises - Protostar - Net 0

In this task we have to work with byte ordering and ways to send/receive them. I wouldn't tell about endianness because there are a lot of good internet sources that cover it. (e.g. wiki ).

Task binary sends a number and waits when we will provide little endian version of it. Our task is to get number from incoming message, convert it into binary form and then send it backwards. To get numbet you will probably want to use regular expression which will cut out contiguous digit string between quotation marks. Then there is a fast solution in Ruby to use pack method of the Array class which allows to convert integer from string to binary. Then we will just send it and receive congratulation message.

Exploit exercises - Protostar - Heap 3

In the heap 3 task 3 portions of memory are allocated on the heap. Then 3 command-line arguments are copied without bounds checking and later the allocated memory is freed. We are supposed to exploit Doug Lea way of allocation and deallocation of memory. There is a nice online page with a description of the way how to exploit it.

Exploitation is based on the fact that while memory is being freed, if there is a free block next to the one that is being freed, free function merges two blocks and write some metadata at the calculated addresses. That means that we can make free function overwrite value at the user provided address after corrupting metadata of the allocated blocks. We should make free think that previous block is free and change metadata to influence address calculation. In the task blocks are allocated in a way that is pictured on the image:

Exploit exercises - Protostar - Heap 2

In this task we are able to control the sequence of malloc and free operations. Also the binary seems to be different from the source because binary allocates not enough memory for the auth struct. If you write auth 1, only 4 bytes are allocated for a whole 36 bytes auth structure. So if we are able to create another structure that has nonzero byte at 32-byte offset we will get a flag. Let's allocate service struct that has unlimited size and therefore can overwrite auth at offset 32 from auth pointer.

Exploit exercises - Protostar - Heap 1

In this task there is a bit more calls to malloc function. As we can see first strcpy is able to overwrite all other allocated data except first allocation. Data allocated in a way that is shown on the picture.

Next strcpy gets address from the allocated memory and write there second argument. So we can overwrite an arbitrary place in memory.
Since main function uses puts function to print something after second strcpy was finished and the fact that winner function doesn't use puts function, we can overwrite address in GOT for puts to move execution flow to the winner.

Exploit exercises - Protostar - Heap 0

Heap 0 level teaches us that variables that are placed in a heap are referenced by different addresses in memory far from stack. Two sequential allocations have a high probability to be one after the other in memory. We can exploit this by overflowing buffer.

Exploit exercises - Protostar - Format 4

Last level of the format section was more interesting. It supposed you to change code execution sequence. Immediately after printf is called there is a call to exit() function. But in order to reuse code in memory there is a PLT(procedure linkage table) that redirects execution to the place according the address of the specified function in GOT (Global Offset Table). Since .plt section in or binary is read-only and jump is made after address dereference we have to change a value that this address references to our value. This article contains very detailed description of PLT, GOT, PIC(Position Independent Code).

Exploit exercises - Protostar - Format 3

Format 3 was quite easy after the way I've tried to solve Format 0 :) . Third task in format section required to write four bytes into specific location in memory.

Exploit exercises - Protostar - Format 2

Format 2 was quite easy, even easier than format 1 for me. All you need is to write appropriate byte to the target address.

Exploit exercises - Protostar - Format 1

Format1 task differs from format0 task in a way where target variable is located. In this case target is located in .bss segment.

Exploit exercises - Protostar - Format 0

This task was quite educating for me. It contained very simple buffer overflow vulnerability that should be done via format string in less than 10 bytes of input.

Exploit exercises - Protostar - Stack 5

After a lot of effort spend on trying to exploit this simple program (http://www.exploit-exercises.com/protostar/stack5) I've finally executed root shell.

Here are some difficulties that I have encountered: