alt Hacker News> The fuzzed program usually crashes because its executable code or the control flow got overwritten directly by the input, or indirectly by the program code itself when it tries to process bad data.
Add assertions to your code. Voila, your run-of-the-mill fuzzer can now hunt for arbitrary problems with your program by turning them into crashes.
When fuzzing C programs, I usually also add undefined-behaviour sanitizers and friends, in the mode where they crash when you run into the kinds of UB they can detect.
Replies
Again, the point of a data-only attack is that you replace, say, a string with another valid string, and take control of program logic that way. For example, imagine a program that uses `system(LS_CMD_STR)`, where that LS_CMD_STR is some kind of constant holding the value "ls -lah". If an attacker can corrupt program memory in such a way that it overwrites that value with "rm / -f", no amount of assertions will trigger on this, but the program will do something much worse than expected.
It's not bad data, that's kind of the point of it.