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Certified Ethical Hacker (CEH) Practice Question

During a penetration test, you find a SUID-root executable /usr/local/bin/backup on a CentOS host. Static analysis shows the binary calls tar -czf /var/backups/www.tgz www through system() without specifying an absolute path. You have write permission in /tmp. What is the most reliable way to leverage this flaw to obtain a root shell?

  • Monitor backup with strace to harvest file activity and brute-force /etc/shadow once root passwords are captured.

  • Create a custom executable named tar that launches /bin/bash, store it in /tmp, prepend /tmp to PATH, then run /usr/local/bin/backup so it executes your payload as root.

  • Set LD_PRELOAD to a malicious shared library and run /usr/local/bin/backup so the library is injected with root privileges.

  • Use ptrace to attach to backup at runtime and inject shellcode into its memory space to gain a root shell.

Certified Ethical Hacker (CEH)
System Hacking Phases and Attack Techniques
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