Linux 3.13.0-32-generic: Exploit

// Create a file we own int fd = open("lower/file", O_CREAT | O_RDWR, 0777); write(fd, "AAAA", 4); close(fd); This is the magic trick. The exploit mounts an overlay filesystem where lower is read-only (where the target file lives) and upper is writable (where changes go).

Posted by: Security Research Team Date: October 26, 2023 (Updated) Difficulty: Advanced Introduction If you have been in the cybersecurity space for a while, you have likely stumbled upon a vulnerability report or an exploit script mentioning a specific kernel string: linux 3.13.0-32-generic . linux 3.13.0-32-generic exploit

This particular kernel version is iconic for a specific reason: it is the default generic kernel for (released April 2014). While ancient today, this kernel represents a golden era for privilege escalation (Local Privilege Escalation - LPE) research. For penetration testers and red teamers, finding this kernel on a target in 2024 is a "sure win." For blue teams, understanding why it is vulnerable is a masterclass in kernel security. // Create a file we own int fd

char opts[256]; snprintf(opts, sizeof(opts), "lowerdir=%s,upperdir=%s,workdir=%s", lower, upper, work); mount("overlay", merged, "overlayfs", 0, opts); Now, inside /tmp/merged , the file file appears. If you edit it, the changes actually go to /tmp/upper/file . This is where the exploit deviates from normal behavior. The attacker creates a second thread. Thread A tries to rename the file from the overlay to a protected location (e.g., /etc/cron.d/exploit ). Thread B constantly churns the filesystem by creating and deleting files in the upper directory. This particular kernel version is iconic for a

For penetration testers: Enjoy the easy win, but document it thoroughly. A root shell via a 9-year-old bug is a clear sign of a broken patch management policy.

uname -a Linux target 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux cat /etc/issue Ubuntu 14.04.5 LTS \n \l

# Compile the exploit gcc overlayfs.c -o exploit -lpthread id uid=1001(bob) gid=1001(bob) groups=1001(bob)