Deciphering the Simple Machine?s Forum audio Captcha

2008.04.30
Risk: Low
Local: No
Remote: Yes
CWE: CWE-264


CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

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


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