I was playing around with Codeforces and inspecting the networking of the website when I decided to check if Codeforces is vulnerable to CSRF (Cross-Site Request Forgery) attacks or not. I found that all requests contain CSRF tokens but I decided to test it anyway. I copied the request to my terminal and removed the CSRF token and it worked! I tried with different requests and apparently the CSRF tokens — although they existed — were never validated. Codeforces was vulnerable to CSRF attacks.

You can read more about it on my blog : http://blog.mbassem.com/2015/05/09/codeforces-account-takeover/

I want to thank MikeMirzayanov for his fast response and fix!

Your comments are welcomed!

Hi All,

Reccently I've seen some very nice tutorials here on Codeforces. Tutorials like Algorithm Gym By PrinceOfPersia should not be lost between other blog posts. I think Codeforces should have a pinned tutorials tab in its navbar. This Tutorials page should contain links to verified tutorials on Codeforces, something that's exactly like Topcoder's tutorials but for Codeforces. I guess this will encourage more people to write tutorials with the motive of getting them added to this tutorials archive. I searched before posting this idea but I didn't find any post that suggests something like this.

What do you think ?

Hi,

I developed a python tool to distributively run GCJ, FB hacker cup — or any contest in which you submit the output file — testcases on several machines. This should theoretically divide the program running time by the number of machines running plus a small network overhead. It's not yet ready for real contest usage but I hope it'll be ready before the next GCJ or FB hacker cup round.

Github Repo : https://github.com/MohamedBassem/dTests

Or you can download it from : https://pypi.python.org/pypi?name=dTests&:action=display

Check the repo for more info, installation and usage guide.

Your ideas and contributions are more than welcome! :)

Hi all,

Is there any way to view my submissions for the problem i'm viewing now other than searching my submissions list for it ? if there isn't I think it would be great if we have a button in the problem's page to view our submissions for this problem.

Thanks :)

Hi All, I'm getting a strange precision error in this problem : 284C - Cows and Sequence and this is my code : 3346105 I know that this problem could be solved by many other ways , but what's wrong with this implementation ? I'm using a segment tree with lazy propagation , every node contains three integers , the value of the node ( which is the summation over this range ) the update flag ( and value ) and the number of leafs under this node.

Thanks :)

UPDATE : The problem was that integers overflow and the size of the vector was causing some problems too , Thanks to EarlOfDitches and here is my accepted solution 3348952 :)

Hi All, I would like to know how to hack a code on Codeforces using a generator , could someone please show me a sample generator that he used before ? Thank You :)

UDPATE : You should print a new line at the end of the generated case , Thank You guys :)