13

If you look at the disassembly of authorize() I'm sure you'll find that the compiler is pushing and restoring more registers than just EBP or aligning the stack. I would recommend that you always look at the disassemly when dealing with overflows of various kinds. The compiler and decompiler, if you use one, hides a lot of details. The disassembly never lies ...


12

First of all, I have bad news for you ! Doug Lea's malloc is almost no more used in any C library implementation (even if understanding dlmalloc can help a lot to understand new ones). The new implementation that is most widely used is ptmalloc2 and the best way to learn about it is... to read the code... So, if you are using a Debian(-like) distribution, ...


11

Why does the return address have to point to the shellcode in the same buffer? It doesn't, but generally, both the shellcode and the return address are delivered at the same time, so they are stuck together for that reason. If your exploit allows you to deliver them separately, then they can be separated. However, they are by necessity both local to the ...


9

Your Stack is totally fine. Look more careful at the values: 0x34333231 0x38373635 0x63626139 0x6337785c 0x3438785c 0x3430785c 0x3830785c which interpreted as an ascii string becomes this. literally: 123456789abc\x7c\x84\x04\x08 As you can see, it's exactly what you entered. And I mean by that, that for example \x7c is the String "\x7c" and not "|". Use ...


8

As far as the screenshot depicts, I can say that you are on the right track. You have correctly, overwritten the Pointer to NextSEH and SE Handler. Some explanation: Exception Registration Record Structure typedef struct _EXCEPTION_REGISTRATION_RECORD { struct _EXCEPTION_REGISTRATION_RECORD *Next; PEXCEPTION_ROUTINE Handler; } ...


8

GDB protects you to overflow your char array. (gdb) p &buffer $25 = (char (*)[512]) 0x7fffffffdfe0 To bypass this security you can either write directly the memory : (gdb) set 0x7fffffffe1e0=0x41414141 Or cast the array as a bigger one and then set your stuff : set {char [513]}buffer="512xA"


7

You don't need to bypass gcc's stack smashing detection. If you overwrite key correctly, you get an interactive shell before the stack check is performed at the end of func(). Here's the proof in the form of a Python script: import socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(("pwnable.kr", 9000)) s.send("A"*52 + "\xBE\xBA\xFE\xCA" ...


7

AFAIR Windows XP does not necessarily crash on heap corruption, you need to specifically turn this behavior on using gflags.exe (from debugging tools) gflags /p /full /enable foo.exe Pageheap.exe might work as well, see http://support.microsoft.com/kb/286470 In any case, the point of exploitation is not to crash the process but to get it to run your code, ...


7

Yes, this is an implementation of what's often called "Stack Canaries", a method of stack Buffer Overflow Protection. That example you're describing is specifically the method used by Visual Studio, enabled by default since Visual Studio 2005, implemented since Visual Studio 2003. It is also called GS protection due to the fact Visual Studio provided the ...


7

On modern systems the most obvious culprit is probably address space layout randomization, but stack frame layout variablity was problematic for exploit development even before ASLR became widely implemented. This was alluded to in AlephOne's venerable "Smashing the Stack for Fun and Profit": The problem we are faced when trying to overflow the buffer of ...


6

This comes down to the type of bug you are exploiting. If your payload cant contain null bytes (a vulnerable strcpy), this can become an issue, however not all bugs have this constraint. Take for example a bug in how a filetype is parsed, which allows null bytes. Also there is the possibility of a series of bugs to be used, for example, the idea of heap ...


6

The answer from Jason is the correct solution. However, I wanted to give an alternative answer without Python, but from the terminal. IMO Python is always preferred for better automation, but sometimes you just wanna have a quick exploit done without extra tools. With that in mind, one's natural attempt would be something like below: echo -e "...


6

first, you should disable ASLR system-wide, you can do this as follows: echo "0" > /proc/sys/kernel/randomize_va_space second, compile your program using flag with -zexecstack -fno-stack-protector -g example gcc program.c -o program -zexecstack -fno-stack-protector -g cheers :)


6

Nothing easier than that. gdb the executable, set a breakpoint at main, have gdb print your buffer. $ gdb /opt/protostar/bin/stack5 (gdb) break main Breakpoint 1 at 0x80483cd: file stack5/stack5.c, line 10. (gdb) run Starting program: /tmp/stack5 Breakpoint 1, main (argc=1, argv=0xffffd674) at stack5/stack5.c:10 10 stack5/stack5.c: No such file or ...


6

First of all, read this: https://www.blackhat.com/presentations/bh-asia-03/bh-asia-03-litchfield.pdf That's pretty much how all this started. A SEH buffer overflow is a specific stack overflow that targets the EXCEPTION_REGISTRATION_RECORD sitting some arbitrary distance down the stack. Why does this not happen for every program then since there should ...


6

Don't worry, the shellcode is executing properly, just that the debugger "skipped" past the execution. Remember that rip is the instruction pointer and whatever code present at the rip is executed. If the code is invalid however, something will go wrong (for example a SIGSEGV will be raised) In this particular case, a S (byte \x53) corresponds to a push ...


5

The only idea I have is to compare the dumps. The places that are same in all dumps are code or read only data. The places that are changing from dump to dump are either stack or section like .bss. After finding places that are not changing I'd try to disassemble these places in order to divide between code and data. I think that the places with the code ...


5

In fact, the memory layout within gdb and outside of it differs of a few bytes. There have been recently a question about this here. You can read: How to predict address space layout differences between real and gdb-controlled executions? In your case, you may just have to adjust your address by adding/subtracting 96 bytes. I can, also, give you a few ...


5

Nope. Metasploit is a pentester framework, not a reversing/malware-dev framework. Instead, you should master a debugger (IDA, Radare2, OllyDbg, etc) and at least one scripting language (Python or Ruby).


5

Yes, this is Microsoft's stack overflow protection, commonly known as "GS cookie". From Compiler Security Checks In Depth: When the function is compiled with /GS, the functions prolog will set aside an additional four bytes and add three more instructions as follows: sub esp,24h mov eax,dword ptr [___security_cookie (408040h)] xor eax,dword ptr ...


4

If I'm understanding your first question correctly, I think there was a disconnect between you and whoever told you that. There is no restriction based on the buffer(s) being in the same process, at least not with respect to return values. You could absolutely have the return address point to the start of the shellcode. It's entirely up to you. The better ...


4

Samurai's answer is correct , but put more clearly , your mistake is that you enter the literal string 123456789abc\x7c\x84\x04\x08 where as what you probably want is something like: perl -e 'print "123456789abc\x7c\x84\x04\x08"' | ./yourbinary In the first case the \x7c\x84\x04\x08 is just that, a 16 characters length string, where in the second case, ...


4

No.               ​


4

I'm sorry, but this certainly works for me. Lets go through this step by step, shall we? 1. Set up I used your command line to compile the program: gcc -z execstack game_of_chance.c -fno-stack-protector -no-pie -m32 -o goc I've done one small change though, I changed #define DATAFILE "/var/chance.data" // File to store user data to #define DATAFILE "...


4

You're doing well, with a little bit help you can exploit this program. First, let's look at stack layout for Linux (i assume it is Linux because of sudo and it is more common than other Unix-like OSes). Sorry for Turkish parts in pictures. old-EIP is not immediately after our buffer. I compiled your program in my 32-bit Linux Mint and as you can see GCC ...


4

We have two major stack protection for buffer overflows: Stack canaries Non-executable stack You land on nopsled but, you get segmentation fault. Because your operating system marked program stack as non-executable and processor raises the exception when program counter addresses that segment. But, even we use executable stack (for GCC use -z execstack) ...


4

First thing that comes to mind when you have non-executable stack is Return-oriented programming which, as the name implies, uses return to execute a code you want. When using ROP, you will want to use the program's executable and dlls (or .so files for linux) and rely as little as you can on system dlls as they change with the OS version. The idea is that ...


3

Metasploit can generate some malicious files, such as PDFs. Malware analysis isn't necessarily just Windows PE files so it might be a good idea to look into other file formats. Metaploit could be useful to generate your own samples to analyze. Msfvenom might be interesting to you as well. It is a tool that generates shellcode given a payload. ...


3

The ROP chain uses gadgets, which are short code snippets performing a basic function. The instruction what you see in the Python script in the video are the gadgets names, which were selected in the beginning. As an example, the XOREAX gadget was a code snippet at address 0x080512c0, which contains the following instructions: xor eax, eax ret So, whet the ...


3

Yes, you can simply jump backwards. Control flow should reach your NOP pad, you can code your trampoline in there.


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