Example buffer overflow11/26/2023 In Windows there is "Data Execution Prevention (DEP)", on Linux OS grsecurity and selinux and on Mac OS the "Mandatory Access Control (MAC)" all designed to prevent buffer overflows from happening or exposing the system. Modern OSs' have their own security measures to limit the impact of buffer overflows vulnerabilities on the system. It is a common source code auditing technique to check proactively the program execution against unhandled errors. In the case, buffer overflow fuzzing can reveal bugs in the source code which can result in unusual program behaviour. This method is usually done with automated tools that feed the program execution with sample data. Fuzzingįuzzing or fuzz testing is a technique used to provide invalid or unexpected data to a program execution. Address Space Layout Randomization (ASLR)ĪSLR is a technique to randomize the position of the stack, executables, and loaded libraries, making it more difficult for attackers to exploit buffer overflow vulnerabities. The processor will prevent code exectution from these memory parts. This way memory segments that are used for data are marked as readable or writable. The NX bit is a processor feature that allows certain memory pages to be marked as non-executable. If there is an absolute necessity to use a non type safe programming language then it is essential for the programmer to be security aware, refrain from using common functions that are vulnerable, and to audit the code before going into production. One easy way to avoid buffer overflows is to use type safe programming languages, although exploitation remains possible through system calls. Preventionīuffer overflows occur to programs where the memory layout is exposed to them. In this case an attacker was able to compromise remotely any mobile phone running Android OS version 2.2+ by simply sending a malformed video that would cause a buffer overflow in the stagefright library and allow the execution of malicious code. One of the most recent and critical bugs that was caused by a buffer overflow was " Stagefright", a bug in the Android OS stagefright library. An equivalent command that mitigates this problem is strncpy which also takes an argument of the size of the source "strncpy (destination, source, srcsize). Next we use strcpy function to write a string into the specified array bigger than what it can hold eventually resulting to a buffer overflow. In the example above we first define an array of type char and size 10. Strcpy(buff, "This is more than the buffer can hold") A practical example of a buffer overflow using the strcpy function would be the following: So if bigger amounts of data are pushed to the destination buffer then it will result in a memory overwrite. Strcpy copies a string pointed by source into the array pointed by destination "strcpy (destination, source)" without checking the length of the source. An example of a vulnerable C function is strcpy. There are different techniques to exploit a buffer overflow vulnerability that vary depending on processor architecture, operating system (OS), and memory region. This vulnerability is common in programs written in the C or C++ programming languages because these languages are designed to allow access to memory. Only native code programs are vulnerable to buffer overflows, meaning programs which use the process instruction set directly rather than intermediates like Java Virtual Machine. In a security context, a buffer overflow can give an attacker access to different parts of the internal memory and eventually control the program execution, introducing risks in confidentiality, integrity and availability. Buffer overflows occur when a program or process tries to write or read more data from a buffer than the buffer can hold. A buffer is a part of the physical memory storage that is temporarily used to store data. A buffer overflow is a bug in a computer program that can lead to a security vulnerability.
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