Exploiting C strstr Function (PicoCTF 2022 #37 'rps')

[@thetrollingboss3155]

Wow, that's amazing! I did not even realize the strstr function was vulnerable during the competition and ended up doing some good 'ol PRNG abuse

[@0xTas]

That was a fun little exercise in reversing a program's logic, nice video.

[@majoryoshi]

The only proper way to win at RPS. I know these are designed to be easier but holy cow this made me laugh so hard at how stupid the answer was

[@Lodinn]

Tbf given a win is possible playing "normally" one might as well just brute force it.

[@kawzaki]

The moment I saw strstr I guessed put all of them in as one word. Funny! Then funny how the flag reads some extreme luck ! Hahaha

[@noideawhatever]

I searched what is strstr and figured the loophole out right away :D

[@mrhappytroll]

Im proud of myself for figuring this out just by pausing and looking at the source code haha

[@bhagyalakshmi1053]

Ok full pics and videos season.

[@djibrille31]

Why does he use the ? sign in the grep command regular expression? Is it not enough to just use the ".*" like grep -oE "picoCTF{.*}". It drives me mad that I do not get it.

[@Lodinn]

If the output contains another closing bracket, greedy capture would get the entirety of it. Not necessary here, but it's a good habit to have when dealing with regex matching something in brackets.

[@lucidattf]

if the text content for example included picoCTF{aaaaa}aaaaa and then another }, the grep without the question mark would output "picoCTF{aaaaa}aaaaa and then another }"

[@bladesvlogs4965]

Would never have gotten that one 🤪

[@AmanPatel-rv2it]

That's nice - just strstr being my cousin 😂😂

[@vanfrancisco4573]

Lmao, i have been tinkering the program only not to notice that the category was not a reverse engineering problem but a binary exploitation problem. stupid me. LOL

[@lordspacecake5565]

Very neat trick

[@jeffer746]

i just spammed the program with paper 5000 times until it won lol

[@unutilisateurdeyoutube1256]

you spam five times rockpaperscissors and it wins xd