CrossCTF_2017: Patching transformer

Category: Defense Points: 100 Description:

Patch the broken transformer! Use the following command curl -v -F secretKey=@localFile 192.168.0.30:8080/api/transformer Binary to patch here

Write-up

This is a really simple one and is easily defeated by nopping most parts of the binary. In this case, we can exploit this by buffer overflowing word 1 with 256 bytes of maximum bytes, followed by 4 bytes of junk, followed by 4 bytes of pointer pointing to stealth().

To patch, all we have to do is to NOP either the scanf operation or even hex edit stealth() to immediately leave & ret. There's no fixed solution.

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