FCrackZip 1.0 – Local Buffer Overflow (PoC)
# Exploit Title: FCrackZip Local Buffer Overflow PoC # Date: September 5th, 2010 # Author: 0x6264 # Software Link: http://oldhome.schmorp.de/marc/data/fcrackzip-1.0.tar.gz # Version: 1.0 # Tested on: Ubuntu 10.04 # CVE : None Software Description: fcrackzip is a zip password cracker, similar to fzc, zipcrack and others. Vulnerability: FCrackZip does not check the length of the input provided to it when using the '-p' flag to supply an initial password or file used for a dictionary attack. Passing it a string exceding its buffer size (40) results in an overwrite. Vulnerable Code: ---------------------------- case 'p': strcpy (pw, optarg); break; ---------------------------- Proof of Concept: $ ./fcrackzip -p $(python -c 'print "A"*44') file.zip Due to being compiled using canaries the overflow is detected and the process is terminated before the overwrite can take place. Solution: Replace the function 'strcpy (pw, optarg);' with 'strncpy (pw, optarg, 40);' Unlike strcpy(), strncpy() will copy no more than the specified string size(40 in our case). |