Deciphering the Simple Machines Forum audio Captcha
The Simple Machine?s Forum audio Captcha that has been hardened from attack.
I have contacted SMF about this flaw and it has been verified.
I go into greater detail of how i am able to break this captcha here:
http://www.rooksecurity.com/blog/?p=6
Exploit Code: http://www.rooksecurity.com/exploits/smf_captcha.zip
This captcha has been broken before and exploit code is available here:
http://www.securityfocus.com/archive/1/471641 . The fix was to add a randomly
generated static.
I was able to write code to decipher the audio file using a Fuzzy Logic
comparison http://en.wikipedia.org/wiki/Fuzzy_logic . The comparison is the
Hamming Distance http://en.wikipedia.org/wiki/Hamming_distance between the
original audio file and the damaged one generated by the Captcha.
peace