Skip to main content

Submitting Flag

CTF challenges require you to submit one or more flags to solve them, these flags are text strings which act as proof of solving. These are obtained when you solve the challenge (i.e. exploit a challenge instance, gain admin access on challenge instance, reverse engineer the the binary provided as attachment etc.).

Submitting each flag shall provide you with points, and these points are summed to determine your total score and position in the contest scoreboard. There can also be flags with zero points, however.

To submit a flag, follow the below steps:

  1. Go to the challenge page (for which you have found a flag)
  2. On the left-side sidebar you will find the Submit Flag box, where you can paste/enter your flag. Ensure that the flag you have found follows the flag format provided, if any.
  3. Click on the flag icon (or press the ENTER key) to submit the flag.
  4. You will receive a confirmation saying whether the flag is accepted, rejected or kept for review.

On successful submission of a flag, you will also see

  • the points you have earned for it.
  • an explanation text, if the organizer/author has set it
  • any challenge unlocked (a list if multiple are unlocked), if the current challenge was a prerequisite for any other challenge

Limits on Attempts​

You may submit flags for a challenge any number of times, as long as the organizer/author has not explicit set a limit. If an explicit limit has been set to the number of flag submissions allowed, then it will be displayed before submitting (i.e. how many chances in total and how many chances are left for you).

Also note that, there is an in-built rate-limiter algorithm that prevents you from attempting too many flags (> 10 attempts/min) in a short duration, which automatically resets. This is an automated system limit, and is kept to protect against brute-forcing of flags as well as to prevent any attack against the platform.

Common Issues​

There can be a variety of reasons why despite solving the challenge your flag might not get accepted. Here are some common issues -

  1. flags are case-sensitive, ensure you paste your flag exactly as you found them.

  2. you might be submitting the flag in wrong flag format or without wrapping it with a flag format (say the flag you got is - 84567dv, but there is a flag format - inctf{...} given, then you need to submit the flag as - inctf{84567dv} instead)

  3. flags can be deactivated by the organizers, in case of which you will simply get a rejected message.

  4. *mistake/typo from the organizers** - It could be also the author mistakenly setting the flag wrong