picoCTF General Skills Guide

Wave a flag

Name: Wave a flag
Description: Can you invoke help flags for a tool or binary? This program has extraordinarily helpful information...
Author: syreal
Tags: Easy, General Skills, picoCTF 2021
Challenge from: picoCTF 2021
Files: warm
Hints:
1. This program will only work in the webshell or another Linux computer.
2. To get the file accessible in your shell, enter the following in the Terminal prompt: $ wget https://mercury.picoctf.net/static/cfea736820f329083dab9558c3932ada/warm
3. Run this program by entering the following in the Terminal prompt: $ ./warm, but you'll first have to make it executable with $ chmod +x warm
4. -h and --help are the most common arguments to give to programs to get more information from them!
5. Not every program implements help features like -h and --help.

Theory

According to the description, to get the flag we have to open an executable file or something to invoke a flag it says, and we'll need to use the help parameter for something. Idk let's just see what the program has.

Solution

First download and run it:

shukularuni-picoctf@webshell:~$ wget https://mercury.picoctf.net/static/cfea736820f329083dab9558c3932ada/warm
--2025-04-17 12:27:29--  https://mercury.picoctf.net/static/cfea736820f329083dab9558c3932ada/warm
Resolving mercury.picoctf.net (mercury.picoctf.net)... 18.189.209.142, ...
Connecting to mercury.picoctf.net (mercury.picoctf.net)|18.189.209.142|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 10936 (11K) [application/octet-stream]
Saving to: 'warm'

warm                                                                100%[=================================================================================================================================================================>]   10.68K  --.-KB/s    in 0s    

2025-04-17 12:27:29 (352 MB/s) - 'warm' saved [10936/10936]

shukularuni-picoctf@webshell:~$ ./warm
-bash: ./warm: Permission denied

Oh, right. We don't have permission to execute the file, we can just bypass that by adding the executable permission to the file:

shukularuni-picoctf@webshell:~$ chmod +x warm

shukularuni-picoctf@webshell:~$ ls
README.txt  warm

shukularuni-picoctf@webshell:~$ ./warm
Hello user! Pass me a -h to learn what I can do!

shukularuni-picoctf@webshell:~$ ./warm -h
Oh, help? I actually don't do much, but I do have this flag here: picoCTF{b1scu1ts_4nd_gr4vy_30e77291}

There we go! That's the flag.

I rated this level as "good"! :3