Sense of Security - Security Advisory - SOS-11-007

vendor:

PHPCaptcha

by:

Phil Taylor from Sense of Security Labs.

5.5

CVSS

MEDIUM

Authentication bypass

N/A

CWE

Product Name: PHPCaptcha

Affected Version From: 1.0.4

Affected Version To: 2.0.2

Patch Exists: NO

Related CWE: Not yet assigned

CPE: N/A

Metasploit: N/A

Other Scripts: N/A

Tags: N/A

CVSS Metrics: N/A

Nuclei References: N/A

Nuclei Metadata: N/A

Platforms Tested: PHP

2011

Sense of Security – Security Advisory – SOS-11-007

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.

Mitigation:

Remove the script securimage_play.php and disable the use of the Audio CAPTCHA.

Source

Exploit-DB raw data:

Sense of Security - Security Advisory - SOS-11-007

Release Date. 20-May-2011
Last Update. -
Vendor Notification Date. 04-Apr-2011
Product. Securimage / PHPCaptcha
Platform. PHP
Affected versions. 1.0.4 - 2.0.2
Severity Rating. Medium
Impact. Authentication bypass
Attack Vector. Remote without authentication
Solution Status. Vendor workaround
(remove securimage_play.php)
CVE reference. Not yet assigned

Details.
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:

http://www.senseofsecurity.com.au/advisories/SOS-11-007.zip
Mirror: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/17309.zip (SOS-11-007.zip)

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
vulnerability.

Solution.
Remove the script securimage_play.php and disable the use of the Audio
CAPTCHA.

Discovered by.
Phil Taylor from Sense of Security Labs.

About us.
Sense of Security is a leading provider of information security and
risk management solutions. Our team has expert skills in assessment
and assurance, strategy and architecture, and deployment through to
ongoing management. We are Australia's premier application penetration
testing firm and trusted IT security advisor to many of the country's
largest organisations.

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The latest version of this advisory can be found at:
http://www.senseofsecurity.com.au/advisories/SOS-11-007.pdf

Other Sense of Security advisories can be found at:
http://www.senseofsecurity.com.au/research/it-security-advisories.php