SatelliteHijack: trace the binary, isolate the validation routine, and invert it to recover the flag.
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Gdb
5 postsrevlocked
Behind the Scenes
revnotes
GDB
Practical GNU Debugger reference for loading, running, inspecting, patching, scripting, and remote debugging programs.
gamepwnlocked
Nostalgia
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Graverobber
Graverobber: trace the binary, isolate the validation routine, and invert it to recover the flag.