Phil Taylor 指出，PHPCaptcha的音频认证有漏洞，即使停用audio认证，用户也可以访问 /secure_play.php 强制通过。
解决办法：删除 securimage_play.php 脚本，并停用audio认证.
PHPCaptcha, also known as Securimage, is a popular Open Source PHP CAPTCHA library. It is also used in popular WordPress plugins such as
the ‘Fast Secure Contact Form’. Insufficient distortion in the audio version of the CAPTCHA allows an attacker to quickly decode the CAPTCHA
by performing basic binary analysis of the generated audio file. The issue is compounded by the fact that even if the audio feature of the
CAPTCHA has been disabled, it can still be accessed by forceful browsing to the /secure_play.php URI.
Proof of Concept.
Proof of concept code that works against the example_form.php page and the MP3 file format provided with the standard PHPCaptcha package
available from www.phpcaptcha.org is available at:
Proof of concept code is only available for the MP3 version of the audio, however the WAV audio format is also affected by the same
Remove the script securimage_play.php and disable the use of the Audio CAPTCHA.
Phil Taylor from Sense of Security Labs.