returntolibc

returntolibc is a technique used in exploit development that allows an attacker to execute arbitrary code by manipulating the control flow of a program to return to a pre-existing function within the standard C library. Instead of injecting shellcode directly into memory, the attacker redirects the program's execution pointer to a useful library function, such as `system()`, `execve()`, or `dup2()`. These functions can then be leveraged to perform malicious actions, like opening a shell or redirecting input/output streams.

The core idea behind returntolibc relies on the fact that many common functions are available in shared libraries linked to most executables. By overwriting a return address on the stack, often through a buffer overflow vulnerability, an attacker can point execution to the entry point of a desired library function. Crucially, the attacker must also arrange for the function's arguments to be present on the stack in the correct format so that the library function executes as intended. For example, to call `system("/bin/sh")`, the attacker would need to place the address of the `system` function and the address of the string "/bin/sh" on the stack.

This technique is significant because it bypasses some security measures that aim to prevent the execution of injected code, such as non-executable stack (NX bit) or data execution prevention (DEP). Since the code being executed (`system()`, etc.) already exists in memory and is part of a trusted library, these protections do not prevent its execution. returntolibc has been a foundational technique in understanding and developing exploits, particularly in the context of binary exploitation challenges and security research.