![]() The prevalence and impact of buffer overflow vulnerabilities have resulted in the creation of many different mechanisms for protecting against them. Despite being one of the best-known types of vulnerabilities, they still commonly appear in applications: they can be very difficult to detect, and even “safe” code can be exploited if an integer overflow vulnerability exists as well. Protecting against buffer overflow vulnerabilitiesīuffer overflow vulnerabilities can be very dangerous, as demonstrated by their high rank in the CWE list. Even if the developer has done their math correctly, an integer overflow vulnerability can enable an attacker to write a value greater than the intended length. A wrong value in the length argument for strncpy will still allow exploitation of a buffer overflow vulnerability. This is because they assume that the developer has correctly specified the length of the data that they wish to have written to the buffer. However, these are not a perfect solution to the problem. Functions like strncpy and strncat take an argument specifying the length of the input that they should copy over and will stop when they reach a null terminator or the maximum length, whichever is sooner. The simplest way to mitigate buffer overflow vulnerabilities is to avoid the use of unbounded write operators. ![]() A malicious user can use this to overwrite the function return address - or other important variable values - and impact the operation of the program. ![]() They don’t know or care how long an allocated buffer is and will happily write beyond its boundaries if they don’t hit a null terminator. These operators are designed to read data into a buffer until they reach a null terminator. Most buffer overflow vulnerabilities boil down to the use of unbounded read or copy operators like strcpy and strcat in C++. This typically is only an issue when dealing with user-controlled data. Buffer overflow vulnerabilitiesīuffer overflow vulnerabilities are created when the developer does not account for and control the potential case where the allocated buffer is not large enough to hold the data that is to be placed in it. As long as the data fits in the allocated variable buffer, then everything works out. When placing data on the stack, a developer can allocate a variable with a set size to hold that data and then fill it with data. If an attacker can rewrite the function return address, they can control the execution flow of the program and potentially convince it to run attacker-controlled malicious code. As shown, a function’s stack includes function arguments/parameters, local variables and the function’s return address. The image above shows a sample program stack. It grows when new values are added to the top of it, like a stack of papers (hence the name). The stack is a region of memory where a program can store values for later use. While both of these can be the victim of buffer overflow attacks, stack-based ones are the best place to begin. When a program is running, this “somewhere” is either the stack or the heap. ![]() Every piece of data on a computer that is used by a program has to be stored somewhere.
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