format-string-exploitation

To exploit a format string vulnerability, you leak stack canaries and libc addresses by using positional format specifiers like %p or %N$p to read values directly from the stack, identifying the correct input offset first. This discloses PIE code pointers and heap addresses.

The best way to overwrite a GOT entry using a format string bug is crafting a payload with %n, %hn, or %hhn specifiers to write controlled values, redirecting functions like printf@GOT to system for code execution. This includes handling 64-bit address layouts.

Yes, you can use pwntools to automate format string exploitation through the fmtstr_payload and FmtStr classes, which streamline offset discovery and automate the construction of arbitrary write payloads for both 32-bit and 64-bit targets.

FORTIFY_SOURCE restricts certain format string writes, but format string exploitation can still bypass it using specific write techniques. The skill covers FORTIFY_SOURCE-constrained write approaches to achieve memory modification despite these compiler protections.

To find the correct stack offset for a blind remote format string attack, you send positional parameters like AAAA%p%p... and analyze the leaked pointers. This discovers the exact offset needed for arbitrary reads and subsequent writes.

64-bit format string payloads fail to write to target memory addresses often due to null bytes in addresses terminating the string early. You must use null-byte-safe payload layouts, placing addresses after the format string to ensure successful %n writes.