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Hack your way through Stripe's Capture the Flag

stripe.com

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Re: Hack your way through Stripe's Capture the Flag

#191

Post by saurik »

a1k0n wrote: post #178
a1k0n wrote: post #120

Earlier quoted context omitted.

ASLR and non-executable stack make level 4 a huge pain in the ass. (But it's not me doing that)

Update: they helped a brother out, and the stack is actually executable on those binaries. I found out after mailing the organizers in exasperation. I was under this impression because newly-compiled binaries had no-exec on the stack, and I was off by a little when I tried to exploit it the first time. Doh!

Ha! Last night I read your comment, assumed you were right, and then came up with a solution that did not assume an executable stack. ;P (I'm actually quite glad, as messing around with the stack would have been much harder.)

Re: Hack your way through Stripe's Capture the Flag

#192

Post by alanstorm »

ghost91 wrote: post #45
jc4p wrote: post #43

Earlier quoted context omitted.

The whole point is that you're supposed to find vulnerabilities in what you have access to and exploit them to view contents of things you don't have permission to.

I replaced the date with my own script, but it still gets executed as level01 user

HINT: For the purpose of this hint we'll assume your script is a bash script. If you've exploited the setuid program to run your script, bash may execute with the elevated permissions, but any program bash runs will run with your permissions.

Re: Hack your way through Stripe's Capture the Flag

#193

Post by lawnchair_larry »

tzs wrote: post #136

The asshole who fork bombed it is boasting on Reddit: http://www.reddit.com/r/programming/comments/q1qii/want_to_t... Anyone else not at all surprised who it is?

I'm surprised. He is usually at least witty or clever when trolling. Forkbombs are pretty unoriginal if you are older than 14.

Re: Hack your way through Stripe's Capture the Flag

#195

Post by saurik »

gdb wrote: post #68
jnorthrop wrote: post #58

Earlier quoted context omitted.

I am. I think their server must be overloaded. I bookmarked the blog post announcing this and I'm going to try again tomorrow.

Yeah, we're rebooting. Should be up in a few more minutes. Sorry about that.

For anyone building something similar, I imagine having an elastic load balancer for TCP port 22 with a health check on a web service that spawns a process as each of the user accounts before returning "good", combined with an auto-scaling group to make certain there are always a couple healthy instances, would be an automated way to keep something like this running through fork bombs.

Re: Hack your way through Stripe's Capture the Flag

#197

Post by velshin »

aero142 wrote: post #182
tzs wrote: post #136

The asshole who fork bombed it is boasting on Reddit: http://www.reddit.com/r/programming/comments/q1qii/want_to_t... Anyone else not at all surprised who it is?

Anyone have any suggestions for preventing this on sandbox systems?

Googling it says limit user processes via /etc/security/limits.conf http://goo.gl/RJJhN

Is it not that simple?

Re: Hack your way through Stripe's Capture the Flag

#200

Post by tzs »

velshin wrote: post #197
aero142 wrote: post #182

Earlier quoted context omitted.

Anyone have any suggestions for preventing this on sandbox systems?

Googling it says limit user processes via /etc/security/limits.conf http://goo.gl/RJJhN Is it not that simple?

I believe that for each level of the challenge, all users were ssh'ing in to the same user account, so even with per-user process limits a fork bomb would use up all the processes available to the competitors at that level.
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