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Stack canaries, named for their analogy to a canary in a coal mine, are used to detect a stack buffer overflow before execution of malicious code can occur. This method works by placing a small integer, the value of which is randomly chosen at program start, in memory just before the stack return pointer.
Here is an example of ANSI C code that will generally cause a segmentation fault on platforms with memory protection. It attempts to modify a string literal, which is undefined behavior according to the ANSI C standard. Most compilers will not catch this at compile time, and instead compile this to executable code that will crash:
Canaries or canary words or stack cookies are known values that are placed between a buffer and control data on the stack to monitor buffer overflows. When the buffer overflows, the first data to be corrupted will usually be the canary, and a failed verification of the canary data will therefore alert of an overflow, which can then be handled, for example, by invalidating the corrupted data.
Stack Overflow is a question-and-answer website for computer programmers. It is the flagship site of the Stack Exchange Network. [2] [3] [4] It was created in 2008 by Jeff Atwood and Joel Spolsky. [5] [6] It features questions and answers on certain computer programming topics.
Uncontrolled format string is a type of code injection vulnerability discovered around 1989 that can be used in security exploits. [1] Originally thought harmless, format string exploits can be used to crash a program or to execute harmful code.
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Visualization of a software buffer overflow. Data is written into A, but is too large to fit within A, so it overflows into B.. In programming and information security, a buffer overflow or buffer overrun is an anomaly whereby a program writes data to a buffer beyond the buffer's allocated memory, overwriting adjacent memory locations.
Allocating more memory on the stack than is available can result in a crash due to stack overflow. This is also why functions that use alloca are usually prevented from being inlined: [2] should such a function be inlined into a loop, the caller would suffer from an unanticipated growth in stack usage, making an overflow much more likely.