destructeur's Sh4ll10

Author:
destructeur

Language:
C/C++

Upload:
2019-05-05 19:39

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Platform:
Unix/linux etc.

Difficulty:
1.5

Quality:
4.5

Arch:
x86-64

Downloads:
15

Size:
8.13 KB

Writeups:
10

Comments:
18

Description

A little crackme so you don't forget that the only thing you can trust is assembler. You don't need to open a debugger for this one.

Comments (18)
Writeups (10)

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b3n on 2019-05-21 22:37: Is the program supposed to segfault? Is the goal to fix the segfault?

destructeur on 2019-05-22 11:45: Yes, the goal is to fix the segfault by submitting the good string. You don't need any patching or debugging for this one. You just need to read the main function to understand the Crackme. Good luck

b3n on 2019-05-23 17:40: Thanks @destructeur, after your tip I was able to correct the segfault and become a "good boy". I'm curious to see the source, though, because the parameters for scanf seem so weird and threw me off the trail for a bit (73 xor 3 ?). Did you purposely do this, or was this some compiler optimization? Really enjoyed the crackme, thanks.

destructeur on 2019-05-23 19:21: I did 's' (0x73) ^ 0x03 on purpose to throw you off so that if you read badly the routine, you could think that the scanf take the parameter '%s'. I don't know if it was your case. I usually don't upload the source code but it can be a good idea for my next crackmes.

b3n on 2019-05-23 19:28: Yep, that little obfuscation threw me off for a bit. Thanks for the explanation.

destructeur on 2019-05-23 19:32: No problem, Good job!

Bilbin on 2019-06-15 05:18: I'll be honest. That scanf was pretty weird. Threw me off a bit, but I got it. Great beginner challenge.

Bilbin on 2019-06-15 05:19: '"

destructeur on 2019-06-15 10:13: Good job Bilbin, but the goal is not to find a XSS on the comment section.

lb on 2019-06-23 12:16: This was my first crackme, thank you for making it :) Was quite a challenge for me. I would really appreciate the source code if you could link it or if you have a git repo?

ker2x on 2019-06-23 13:06: Are you sure that it's a level 1 challenge ? the algorithm isn't that difficult but finding the actual answer that works... well... i gave up.

destructeur on 2019-06-23 18:10: @ker2x: Try to look at the arguments of the function scanf, think about what you can write in the input to print the good boy.

ker2x on 2019-06-24 20:19: I see what you do clearly (i think so), but solving this whole mess of MOV,ADD,XOR,LEA to have the correct value in RAX ... ugh...

destructeur on 2019-06-25 09:25: @ker2x: Can you identify the arguments of the function scanf (the buffer, and the specifier used http://www.cplusplus.com/reference/cstdio/scanf/)? If so, you will have to read instruction by instruction to understand what is going on and how the program use your input. I can't really help you to read assembly instructions but there are many documentations on the Internet. If after a while, you can't still understand what is going on, don't stay stuck and use a debugger.

Antricks on 2019-07-17 17:02: Oh boy you really fooled me first.. But a really nice crackme. I solved it in the end :D

BinaryNewbie on 2019-07-27 06:44: @destructor, nice one, it took me some time, but it was a funny exercise. I think that i found the correct string and i will submit a write-up soon. Thnx.

Bkamp on 2019-12-02 05:00: This crackme was really good! Lucky for me I totally missed the scanf thing and looked straight at the call rax function. Which I thought was weird. Got it shortly after. Really great exercise for getting used to your debugger :)

bitrot on 2022-02-02 17:31: I'm not sure this is a level 1 difficulty. I realize it's subjective, but I completed four or five "level 1" binaries so far and this was the toughest. Mainly due to the fact that I had to ramp up my debugging skills because I don't yet know ASM that well yet. Also, I think the quality here is very high - five. I'd be interested in the source too, if you ever post it. Thanks for making this one. Very fun.

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Solution by goodBoy on 2019-05-21 17:18:

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Solution by hikilaka on 2019-06-01 03:03:
The solution is explained in the text file.

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Solution by ck on 2019-06-08 16:52:

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Solution by karubabu on 2019-06-13 02:21:
thank you for this crackme!

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Solution by BinaryNewbie on 2019-07-27 07:12:
It contains the flag and a write-up about the solution.

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Solution by ezman on 2019-10-13 12:22:
stepped through the program, found what the program does with the input, then calculated the correct input.

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Solution by Bkamp on 2019-12-02 04:56:

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Solution by m0xz on 2019-12-04 08:43:
Many thanks, had a blast with this. The %p made me waste a lot of time haha

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Solution by Mime on 2020-01-20 18:26:
I tried to make an highly detailed walktrough of this crackme. I hope it can help some newcomers. Good crackme tho !

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Solution by Kryptoenix on 2021-09-05 14:11:

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crackmes.one

crackmes.one

destructeur's Sh4ll10