247CTF - An Impossible Number

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Find a number that is one more than itself. Specifically, a number where n > 0 && n > (n + 1).

Vulnerability

Integer overflow! In languages with fixed-size integers, the maximum value when incremented wraps around to the minimum negative value.

For a 32-bit signed integer:

  • Maximum value: 2147483647
  • 2147483647 + 1 overflows to: -2147483648 (negative)

So the condition n > (n + 1) becomes true.

Solution

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nc 287ab557f3f29afd.247ctf.com 50088
2147483647
247CTF{********************************}

Simply send the maximum 32-bit signed integer value.

247CTF{38f5daf742a4b3d74b3a7575bf4d7d1e}