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Tag: Process Filesystem

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Process Filesystem

The Process Filesystem (procfs) is a virtual filesystem that allows process and kernel information to be accessed as files on systems such as Linux.

In CTFs, players aim to obtain the flag by reading information under /proc/self/ or /proc/<pid>/, such as the state of a running process, environment variables, and command-line arguments. (automatically translated from Japanese)

minaminao
·Updated Apr 24, 2026
Process Filesystem Challenges
FLAG OVER
minaminao

minaminao

Misc
120 solves
permission denied 3
minaminao

minaminao

Misc
101 solves
invisible-grep
minaminao

minaminao

Misc
42 solves
NetFS 2
ptr-yudai

ptr-yudai

Misc
3 solves

permission denied 3

Daily AlpacaHackTopic: File PermissionReleased: May 7, 2026

101 solves
Misc

by

minaminao

minaminao

cat: flag.txt: No such file or directory

Beginner Hint 1 (AI-translated)
  • When you connect with nc, you'll see that a shell is launched.
  • Reading chal.sh, you can see that flag.txt is created with permission 400 before the shell starts.
  • Then all files in the current directory are deleted by rm *.
  • After that, a shell is launched via sh.
  • Of course, running cat flag.txt results in No such file or directory, so you can't read the flag directly.
  • So, how can you read the flag?
Beginner Hint 2 (AI-translated)
  • flag.txt is completely gone, but it wasn't the only file that contained the flag.
  • Think about chal.sh, which also contained the flag.
permission-denied-3.tar.gz
descriptionsolveswriteups