From Wikipedia, the free encyclopedia

A return-to-libc attack is a computer security attack usually starting with a buffer overflow, in which the return address on the stack is replaced by the address of another instruction, and the correct portion of the stack is overwritten to provide arguments to this function. This allows attackers to call pre-existing functions without the need to inject malicious code into a program.

The shared library called "libc" provides the C runtime on UNIX style systems. Although the attacker could make the code return anywhere, libc is the most likely target, as it is always linked to the program, and it provides useful calls for an attacker (such as the system() call to execute an arbitrary program, which needs only one argument). This is why the exploit is called "return-to-libc" even when the return address may be in something named completely differently.

A non-executable stack can prevent some buffer overflows, but not a return-to-libc attack: only existing, executable code is used. On the other hand, these attacks can only call pre-existing functions. Stack-smashing protection can prevent or obstruct exploitation, as it can detect the corruption of the stack and possibly flush out the compromised segment. Address Space Layout Randomization (ASLR) makes this type of attack extremely unlikely to succeed on 64-bit machines, as the locations of all functions in memory are random; however, Shacham et al. show that on 32-bit machines ASLR provides little benefit.

• Buffer Overflow
• Stack buffer overflow
• Stack-smashing protection
• No eXecute (NX) bit
• Address space layout randomization

Certain Host-Based Intrusion Prevention products can provide specific protection from Return-to-LIBC attacks.

• Shacham, Hovav; Page, M.; Pfaff, B.; Goh, E.; Modadugo, N.; Boneh, D. "On the Effectiveness of Address-Space Randomization". Proc. of CCS 2004. 

• Bypassing non-executable-stack during exploitation using return-to-libc by c0ntex at InfoSecWriters.com