DANGEROUS C Functions gets & strcpy (PicoCTF 2022 #04 buffer-overflow0)

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[@jlm1144]

I was at that part in my Security+ chapter about buffer-overflow and I was looking for an example of what it really did in C. Thanks man !! :)

[@JB4lly]

Maybe putting -fstack-protector when compiling would have worked? Not sure

[@mrnord1989]

Thank you John, every time I watch one of your videos I always learn something new :)

[@wChris_]

it seems to be a kali linux thing having no stack-protector when building with gcc, as it works on my machine (ubuntu)

[@FunkadelicFeed]

You have to pass “fstack-protector" when compiling with gcc

[@jpierce2l33t]

Dude, following along right with you, even going ahead now until I get stuck! Please keep going, this is great and I appreciate you so much!

[@greyether777]

Thanks John. We appreciate how you thoroughly explain everything and keep it simple at the same time. You're a rockstar!!

[@Talyzeni]

These videos are so awesome. Thanks so much John

[@wilcosec]

Great series! Keep it coming!

[@VA3KAMA3]

Super cool series, always a pleasure to watch them! Keep it up!

[@windows74001]

Haha I'm a noob at these CTF challenges and had troubles solving this one for some reason. Looking through it with your guidance I'm like "Wow I'm an idiot, it was so simple" lol

[@zer001]

This was fun! Please more John. :)

[@KGAD0831]

Loving this series, John. Please finish it!

[@logiciananimal]

3 ways to fail the computer systems course I did ~20 years ago: 1) cheat 2) do way too little adequate work 3) use gets()

[@tuxmaster2715]

You the best John, thanks a lot for these material and your explanations,
You are a master mind my friend

[@kaleabalemayehu]

you already know it but let me tell you one more time YOU ARE AWESOME.

[@LDowning0190]

Enjoyed the video. Keep them coming.

[@masudrahman253]

Done Watching Cool Thanks John

[@sunriser_yt]

I wanted to subscribe, but I've completely forgotten that I already was. Anyway, thanks for another informative video!

[@henrym5034]

Thank you for all the beginner-friendly content
A question as an absolute newbie into binary: only an input of length>=20 causes the SIGSEGV, i.e. it doesn’t happen with say 17. Is there a way to know or estimate how many more bytes I need?

[@hedgechasing]

The segfault is triggered by overwriting the return address on the stack (changing its value to some random garbage makes the program try to jump to that address and read code from there which the OS does not allow and sends the segfault signal) how many bytes you need to modify depends on the layout of the stack. You can use a debugger and look at the addresses of the local variables or look at the disassembly to see how much space is being allocated on the stack, but in this particular case the extra four bytes are the space on the stack for the local variable input. The layout of the stack is return address, then input then the buffer (though the stack grows down so these end up at decreasing addresses). When you put an input less than 16 characters it fits into the buffer. If you put 16-19 characters it starts clobbering the local variable input, and only once you put in 20 or more characters does it start touching the return address and cause the segfault.

[@henrym5034]

@@hedgechasing thanks for the explanation! I definitely have to look at it more

[@drioko]

Awesome

[@anmoldeepsingh9281]

i think the stack smashing wasnt detected probably the way gcc was compiled, its default could have been -fno-stack-protector, so default build task will never include a canary

[@cqundefine]

sigsegv stands for signal segmentation violation

[@TehPwnerer]

Oh the days I coded in C/C++, flush of output buffer is not guaranteed without the flush

[@zer001]

I think strcpy is the most used function to demonstrate bufferoverflows.

[@MiguelDevOps]

6:34 a minor correction: the char array buf1 is 100*sizeof(char) Bytes long

[@frixx22]

If this is training wheels, I am still at the crawling phase XD. I'll get there one day :')

[@stopper0203]

I don't understand how just adding a few extra characters causes the flag to magically appear. Is it because added the extra characters causes some specific code to execute? If so which part?

[@adilbougma3114]

This is rust will dominated the c language 😂😂 but hey nice reverse engineer 😀 😉

[@acidopcodes]

I gave the 69th like 😁

[@sorrefly]

09:00 laughs in format string vulnerability and return-to-libc

[@fjr2go]

Nice'n'easy :)

[@krgrief]

you don’t explain how the buffer overflow even works though..?

[@rsvv6828]

What is the version of Sublime text you are using?? Please answer

[@Pixailz]

Do you have references / explanation about the {,_COMPLETE}, i searched all day long on Shell expansion and no one say a thing about this tips :)

[@iyousef46]

It's a bash feature called brace expansion.

[@Angel-Pizzaeater]

[@roachxyz]

Is overflow on this the same as overflow on Hacknet?

[@guilherme5094]

👍

[@BrAiNeeBug]

you made a 64bit version, so there more buffers i think.

[@ethanrodrigo4060]

How can this be dangerous?

[@OmarHosam203]

2nd?

[@alier3217]

NVIDIA should be tried for unfair profit and hoarding...

[@inquisitivemanipulator776]

1st?