picoCTF Writeup picoGym Practice Challenges Forbidden Paths (注意<spoiler>)

Forbidden Paths

Description
Can you get the flag?
Here's the website.
We know that the website files live in /usr/share/nginx/html/ and the flag is at /flag.txt but the website is filtering absolute file paths. Can you get past the filter to read the flag?

ウェブサイトは絶対ファイルパスをフィルタリングしています。->相対パスで入力してやれば良い

../../../../flag.txt

picoCTF{7h3_p47h_70_5ucc355_6db46514}