AngstromCTF_2018: Accumulator

Category: Binary Points: 50 Description:

I found this program (source) that lets me add positive numbers to a variable, but it won't give me a flag unless that variable is negative! Can you help me out? Navigate to /problems/accumulator/ on the shell server to try your exploit out!

Write-up

This is a simple integer overflow challenge, with 32-bit integers.

$ ./accumulator64
The accumulator currently has a value of 0.
Please enter a positive integer to add: 2147483647
The accumulator currently has a value of 2147483647.
Please enter a positive integer to add: 1
The accumulator has a value of -2147483648. You win!
actf{signed_ints_aint_safe}

Therefore, the flag is actf{signed_ints_aint_safe}.

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