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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.
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.
A stack buffer overflow can be caused deliberately as part of an attack known as stack smashing. If the affected program is running with special privileges, or accepts data from untrusted network hosts (e.g. a webserver ) then the bug is a potential security vulnerability .
A "return-to-libc" attack is a computer security attack usually starting with a buffer overflow in which a subroutine return address on a call stack is replaced by an address of a subroutine that is already present in the process executable memory, bypassing the no-execute bit feature (if present) and ridding the attacker of the need to inject their own code.
Buffer overflow – out-of-bound writes can corrupt the content of adjacent objects, or internal data (like bookkeeping information for the heap) or return addresses. Buffer over-read – out-of-bound reads can reveal sensitive data or help attackers bypass address space layout randomization .
It did this by using a long string of the repeated letter 'N' to overflow a buffer, allowing the worm to execute arbitrary code and infect the machine with the worm. Kenneth D. Eichman was the first to discover how to block it, and was invited to the White House for his discovery.
A NOP-sled is the oldest and most widely known technique for exploiting stack buffer overflows. [2] It solves the problem of finding the exact address of the buffer by effectively increasing the size of the target area. To do this, much larger sections of the stack are corrupted with the no-op machine instruction.
Buffer overflow is one of the most common programming flaws exploited by computer viruses, causing serious computer security issues (e.g. return-to-libc attack, stack-smashing protection) in widely used programs. In some cases programs can also incorrectly access the memory before the start of a buffer.