picoCTF Writeup: plumbing

出力を制御する技術を知ろう問題

• ジャンル: General Skills
• 難易度: Medium

Writeup

問題文

Sometimes you need to handle process data outside of a file. Can you find a way to keep the output from this program and search for the flag?
Connect to fickle-tempest.picoctf.net 55636.

[訳]

ときどき、あなたはファイルの外のデータを取り扱う必要があります。プログラムのアウトプットを維持しながら、flagを探す方法がわかるかな？fickle-tempest.picoctf.net 55636 に接続してください。

ncで接続します。

▶ nc fickle-tempest.picoctf.net 55636 | head 
I don't think this is a flag either
Not a flag either
Again, I really don't think this is a flag
I don't think this is a flag either
Again, I really don't think this is a flag
I don't think this is a flag either
Not a flag either
I don't think this is a flag either
I don't think this is a flag either
Again, I really don't think this is a flag
...

ビャーっと出力が出てきました。

▶ nc fickle-tempest.picoctf.net 55636 | wc -l  
   10002

10002行です。
picoCTFでgrepしてみます。

▶ nc fickle-tempest.picoctf.net 55636 | grep picoCTF
picoCTF{digital_plumb3r_XXXXXXXX}

あら？あっさりflag取れました。(flagはマスクしています。)