Questions tagged [c]

The C programming language, commonly used for low-level programming

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how to get this into a stack oveflow performed into integer overflow?

I'm trying to understand stack buffer overflow performed by an integer overflow , and am working with a simple piece of code, as below, but however I am not sure how can I add to this code an integer ...
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1answer
162 views

Write a Python or C program to guess the key [closed]

Key generation program in C: #include <stdio.h> #include <stdlib.h> #include <time.h> #define KEYSIZE 16 void main() { int i; char key[KEYSIZE]; printf("%lld\n", (long long) ...
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Libcap filter is not filtering the right packets

I am trying to do 'rst hijacking' by using a c script with libcap and libnet included. I use libcap to sniff all packets coming from and going to a host given as input to the program via the ...
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83 views

Buffer bomb level 3 - Prevent stack corruption

I am trying to complete level 3 of buffer bomb lab. The task is to supply an exploit string that will cause getbuf to return my cookie (0x4b64b076) back to test, rather than the value 1. The exploit ...
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1answer
70 views

EIP pointing to shellcode but shellcode is not executing?

I have successfully overwritten the EIP register (pointing to my shellcode) but the shellcode is not executing. I compiled with the command gcc -g -fno-stack-protector -z execstack -no-pie vuln.c -o ...
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75 views

How to disabel relro to overwrite fini_array or .got.plt element?

I am reading the book Hacking: The art of exploitation and there is a format string exploit example which attempts to overwrite an address of the dtors with the address of a shellcode environment ...
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162 views

Is overbuffered done on 10th byte past alocated space?

I am reading The Shellcoder's Handbook, and having trouble with an exercise. I am trying to jump to an address after I exceed the buffer space. After 36 bytes I write a 4 byte payload with an address ...
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2answers
163 views

DLL injector in C doesn't inject the DLL

I am trying to write a DLL injector to perform a DLL injector on a calculator process. I wrote the DLL injector program in C and the DLL but the injector doesn't inject the DLL or any other DLL (I ...
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1answer
163 views

Buffer Overflow in the C program

I'm preparing for an introductory information security examination in university and this is one of the examination questions on Secure Programming. Here is the question. Sorry the original condition ...
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1answer
173 views

What are the security implications of invalid free()?

CVE-2009-5030 OpenJPEG: Heap memory corruption leading to invalid free The tcd_free_encode function in tcd.c in OpenJPEG 1.3 through 1.5 allows remote attackers to cause a denial of service (...
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2answers
83 views

How do I program a function to generate a secure Block Cipher Encryption-Key?

I am currently studying the most widely known encryption algorithms and methodologies. For practice purposes, I want to implement everything from ECB to RSA as some kind of a C crypto library. How ...
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365 views

C/C++ code injection

I know how we do code injections with scripted languages like JavaScript, SQL, PHP, etc. and pretty much wherever a execute() function is used. However, I'm still unsure about how code injection works ...
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Windows shellcode not working in C

I have been trying to run a raw piece of shellcode collected on the net within a C wrapper to try it but it never works... I know the shellcode below is all right because it does work in the context ...
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2answers
93 views

Buffer Overflow

I am trying to overflow the buffer shown bellow, yet can never reach it. I know that the location of buf is before i and len, and in my case to overload the return instruction I need to amend the ...
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82 views

Is a Buffer Overflow / NOP Slide possible for memory addresses that contain null bytes?

I have been reading up on Buffer Overflows and NOP Sleds. I tried to use the exploit on an example target and I got stuck because I needed to inject a null byte in the return address for my BP so that ...
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60 views

Failure to execute shellcode

I'm trying to understand exploits that hijack the execution flow. Before exploiting a buffer overflow vulnerability, I'm just trying to set an environment variable to my shellcode and jump to it. So, ...
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3answers
259 views

Prevent finding key in C++ application binary

I need to store a key (symmetric-key cryptography) within my C++ application binary (based on OpenCV) so that the key as unidentifiable as possible. Can someone help me choose the key so that is ...
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52 views

Confusing with the exact location of a shellcode in memory?

When we test a shellcode, we add it to a small C program and execute it in order to see it does the actual job we expect. But most of the time, it crashes saying 'segmentation fault'. I got the same ...
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1answer
132 views

Stack address is shown less than heap address in C program

I am learning binary exploitation from "Hacking: The Art of Exploitation". In theory the address of an element of stack should be higher than the address of an element on heap. But in this program I ...
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70 views

Side channel resistant of Intel TinyCrypt library

Is the TinyCrypt library side channel resistant. I found a mentioned in the "Genral Remarks" on github. But it is mentioned that it is not fully side channel resistant. Does anyone know the extend ...
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66 views

Why is unistd's getpass unsafe?

While reading about how to properly ask a user for a password in CLIs, this SO answer and this SSE answer recommend the usage of unistd's getpass. However, this function is being documented as ...
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2answers
584 views

Buffer overflow exploit with python3 : wrong return address written

I'm trying to exploit a simple buffer overflow with gdb and peda, I just want to rewrite the return address with the address of a function of the program. I can easily do it with python2 but it seems ...
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1answer
4k views

Does a single fopen introduce TOCTOU vulnerability?

I'm actually fixing driver under Linux. Klokwork said that code like: file = fopen(fileName, "w+"); // w+,r,a and any mix of those is used here if (file != NULL) { /* do things*/ } else { /* throw ...
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2answers
214 views

In Return-Oriented Programming how can the machine execute unaligned instructions?

I am reading "The Geometry of Innocent Flesh on the Bone: Return-into-libc without Function Calls (on the x86)". The author claims that x86 code is like English written without punctuation or spaces, ...
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1answer
79 views

How and why is executable stack dangerous?

I'm currently using nested functions (which is extensions to C in GCC), however that is not supported (and is not planned to be supported) in clang. Mostly on the grounds that executable stack is ...
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205 views

Creating X509 certificate in C using post-quantum public key algorithm?

I'm trying to implement a self signed x509 certificate that uses a post-quantum (PQ) public key algorithm as the public key algorithm. I looked at the openssl library in c, and the way it's done using ...
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1answer
203 views

Shellcode as part of format string buffer

I'm currently trying out a simple format string vuln exploit. The target program looks like this: int main(int argc, char *argv[]) { char buffer[1024]; strncpy(buffer, argv[1], sizeof(buffer)...
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41 views

How to find out what program called an API in windows?

Okay, so I am developing a kernel module that does kernel mode hooking to hook APIs and modify some values. But is there anyway I could tell if what program called a specific API? Say a program from ...
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3answers
669 views

If x86 architecture has overflow flag in the CPU, then why can't we use it to detect integer overflows in C binaries? [closed]

I'm talking about the overflow flag that is used in some architectures like x86: https://en.wikipedia.org/wiki/Overflow_flag why aren't operating systems using this overflow flag to stop integer ...
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171 views

ettercap packet modification

I am trying to figure out how to write a plugin in ettercap which modifies the payload of a packet. I have a vm with a simply python socket server and a simply python client on the ettercap machine. ...
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1answer
346 views

Is zeroing out values on the stack and arguments overkill?

I generally zero out memory the moment it's served its usefulness, but only with heap-allocated chunks. Is it a sin (or overkill) to do the same with arguments and stack values? Thanks in advance. ...
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1answer
344 views

Why in LD_PRELOAD exploit we call unsetenv(LD_PRELOAD)?

Why to exploit LD_PRELOAD like is shown here https://touhidshaikh.com/blog/?p=827 in the .c file the first instruction is unsetenv(LD_PRELOAD)? Is it a routine action which all shared libraries do? Or ...
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270 views

Format String Vulnerability - Can't read an address from stdin with read() in C

I wanted to exploit this code using format string vulnerability: int jackpot; void fmt_str(void) { char buf[128]; puts("Give me a string to print"); read(0, buf, 128); printf(buf); ...
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1answer
1k views

Problem with overwriting the return address (buffer overflow)

I'm trying to exploit the following code with a buffer overflow and make it run the overflowed function: #include <string.h> #include <stdio.h> void overflowed() { printf("%s\...
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2answers
145 views

How is executable shellcode inserted?

How is shellcode (the payload) added to an executable file? Assume it is close source. How does the hacker then get the address of where it is? They need this for when they overwrite the return ...
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49 views

What makes detection of optimized-away memory clearing non-trivial?

In this 35C3 talk, it is said that while it is possible to manually inspect whether a package optimizes away memset() that clears sensitive memory, doing it automatically would be challenging. ...
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117 views

Exploiting a Heap Overrun Vulnerability

I am really trying to understand the concept of the attack made possible by the code given below. I notice that strcpy is being used, which does not perform any boundary checks and therefore enables ...
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334 views

Buffer overflow shellcode placement

Sorry if this post is in the wrong section I'm fairly new to the security field and I am new to stackexchange if this post is in the wrong section would be great if it was moved for me,also sorry if ...
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2answers
1k views

Example of a double-free vulnerability in C

I hope this is the correct forum to ask for the question that I have: We are currently discussing double-free vulnerabilities in our software security class, which is why I know the code given below ...
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66 views

Limited ESP Length in Buffer Overflow Sample C Program

May I know how to increase the length of ESP on a sample c program which allows me to execute shellcode on the stack. However, as of now, the sample c program only has an ESP length of 61 thus ...
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1answer
990 views

How does this simple buffer overflow work?

I've got this simple code vuln.c #include <stdio.h> #include <string.h> int main(int argc, char** argv) { char buffer[500]; strcpy(buffer, argv[1]); printf("%s", buffer); ...
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2answers
137 views

If C uses shared libraries, is it possible to write a program that will modify the code that opens a file

If C uses shared libraries, is it possible to write a program that will modify the fopen function to execute a malicious code? How can the OS protect the user from this?
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2answers
1k views

Privilege Escalation: C functions setuid(0) with system() not working in Linux

Quick disclaimer: I fully understand that the code I am attempting to write is insecure, and allows for arbitrary users to escalate to root. I am writing a simple C program like this to demonstrate ...
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520 views

Segmentation fault in exercise program

I am going through this video on buffer overflows but am having some trouble replicating the demo. The issue is that I am getting a segmentation fault when I expect to get a shell at the end. The idea ...
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1answer
899 views

BufferOverflow attack Segment Fault

I'm trying to exploit simple stack overflow vulnerability. But I have trouble writing the exploit.c file. After getting the stack pointer using __asm__("movl %esp, %eax"), I put the address and ...
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1answer
64 views

Buffer Overflow protections in custom library

Does a custom library affected by a buffer overflow need to be compiled with protections even if it is linked against an executable which already has protections?
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1answer
2k views

How to find address of system() in an executable - ROP exploit

I'm trying to find the address of system() in a code repo that I'm trying to exploit using Return Oriented Programming (for a course project). The code has included stdlib.h but it has not used system(...
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555 views

How to find the return address when performing an overflow

for an assignment I'm trying to find exploits in a c program. I found one in strcpy, which is vulnerable to overflow attacks. The problem is I am actually having trouble deploying the shellcode ...
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1answer
145 views

CWE-234 - Snprintf Missing Parameter issues

We are scanning a third party library using a well know static analysis tool here. We keep getting: "Failure to Handle Missing Parameter CWE ID 234" I'm not a C developer but I can't see what is ...
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1answer
340 views

“Hacking The Art of Exploitation” - format string exploit memory truncation

I am attempting the printf() format parameter exploit where providing the user controlled data directly as the sole argument of the printf("user input") allows for the user to provide format ...

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