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What is Canary value in stack What is its purpose?
A stack canary is a value placed on the stack so that it will be overwritten by a stack buffer that overflows to the return address. It allows detection of overflows by verifying the integrity of the canary before function return.
Do stack canaries prevent overflow?
Stack canaries were invented to prevent buffer overflow (BOF) vulnerabilities from being exploited. Buffer overflow vulnerabilities occur when no bounds checking is being done on buffer operations. Functions such as gets() and strcpy() do no such bounds checking.
What is stack smashing detected?
Stack smashing is a form of vulnerability where the stack of a computer application or OS is forced to overflow. This may lead to subverting the program/system and crashing it. A stack, a first-in last-out circuit, is a form of buffer holding intermediate results of operations within it.
Do stack canaries prevent return to libc buffer overflow attacks?
First of all, stack canaries only protect against return address smashing through buffer overflows. But there are other ways to corrupt memory: indirect pointer overwrite or format string vulnerabilities to name two. Second, stack canaries may be bypassed by overwriting them with the original value.
How can stack overflow be prevented?
One method to prevent stack overflow is to track the stack pointer with test and measurement methods. Use timer interrupts that periodically check the location of the stack pointer, record the largest value, and watch that it does not grow beyond that value.
Where is canary on stack?
Similar to the canaries used in coal mines, a stack canary is a variable with a special value placed at the end of the stack memory. Assuming that an exploit with a stack buffer overflow will very likely overwrite that canary, it can be detected by the by the running program.