Demo: Flip the Lock (heap-0)¶
A warm-up heap overflow, solved together with the teaching assistant at the start of the session.
The program keeps two things on the heap: a diary entry you may write to, and a lock_state variable the author is sure you cannot reach.
"My data isn't on the stack, so it must be safe... right?"
You win as soon as lock_state is no longer "shut".
Together with the teaching assistant you will run the binary, read the two heap addresses it prints, work out how far apart they are, and overflow the diary entry far enough to change lock_state.
Files¶
chall.c— the challenge source code.chall— the compiled binary.flag.txt— a placeholder flag, so./challworks locally. It is not the real flag.
Running it¶
Locally:
Against the deployed service, with netcat — type the same things you would type locally:
Hint¶
How far is the diary entry from lock_state?
Use "Print Heap", read the two addresses, and subtract.
Submit the flag: https://ctf.security.cs.pub.ro/so