Cyber Apocalypse
2024
BoxCutter
You've received a supply of valuable food and medicine from a generous sponsor. There's just one problem - the box is made of solid steel! Luckily, there's a dumb automated defense robot which you may be able to trick into opening the box for you - it's programmed to only attack things with the correct label.
Reversing
300 points
Walkthrough
We start by downloading the source files.
We are given a binary
boxcutter
. We start by looking at the binary in Ghidra.It looks like the binary does some calculations and then tries to open a file with that calculated name:
{
undefined8 local_28;
undefined7 local_20;
undefined uStack_19;
undefined7 uStack_18;
int local_10;
uint local_c;
local_28 = 0x540345434c75637f;
local_20 = 0x45f4368505906;
uStack_19 = 0x68;
uStack_18 = 0x374a025b5b0354;
for (local_c = 0; local_c < 0x17; local_c = local_c + 1) {
*(byte *)((long)&local_28 + (long)(int)local_c) =
*(byte *)((long)&local_28 + (long)(int)local_c) ^ 0x37;
}
local_10 = open((char *)&local_28,0);
if (local_10 < 1) {
puts("[X] Error: Box Not Found");
}
else {
puts("[*] Box Opened Successfully");
close(local_10);
}
return 0;
}
We can run the binary with
gdb
and set a breakpoint at the open
call (b *main+0x70
) to see what the calculated filename is.Looking at the registers we can find the flag:
HTB{tr4c1ng_th3_c4ll5}
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