CVE-2008-3573 in Pligg
Summary
by MITRE
The CAPTCHA implementation in (1) Pligg 9.9.5 and possibly (2) Francisco Burzi PHP-Nuke 8.1 provides a critical random number (the ts_random value) within the URL in the SRC attribute of an IMG element, which allows remote attackers to pass the CAPTCHA test via a calculation that combines this value with the current date and the HTTP User-Agent string.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/19/2025
The vulnerability described in CVE-2008-3573 represents a critical weakness in CAPTCHA implementation within web applications, specifically affecting Pligg 9.9.5 and potentially Francisco Burzi PHP-Nuke 8.1. This flaw fundamentally undermines the security mechanism designed to distinguish between human users and automated bots by exposing a predictable random value within the CAPTCHA image URL. The security implications are severe as this vulnerability directly enables automated attackers to bypass CAPTCHA protections through systematic calculation rather than requiring manual solving of visual challenges.
The technical flaw lies in the predictable nature of the ts_random value used in the CAPTCHA implementation. When the CAPTCHA image is generated, the system embeds a timestamp-based random value within the URL's SRC attribute of the IMG element. This value, combined with the current date and HTTP User-Agent string, creates a calculable pattern that attackers can reverse-engineer. The vulnerability specifically relates to weak entropy in the random number generation process, where the ts_random value does not provide sufficient unpredictability to serve its intended security purpose. This weakness is categorized under CWE-330 Use of Insufficiently Random Values, which addresses the improper use of random number generators in security-critical contexts.
The operational impact of this vulnerability extends far beyond simple bypass of CAPTCHA mechanisms. Attackers can systematically automate the process of passing CAPTCHA challenges, enabling them to perform malicious activities such as spam posting, account creation, and form submission at scale without human intervention. This capability directly undermines the web application's ability to prevent automated abuse, potentially leading to data corruption, service degradation, and reputational damage. The vulnerability also affects the integrity of user authentication systems, as it allows attackers to circumvent security controls designed to verify human interaction. From an attack perspective, this represents a low-effort, high-impact method that aligns with ATT&CK technique T1213.002 (Data from Information Repositories) and T1499.004 (Unsuccessful Technical Impact) where the attacker gains unauthorized access through predictable security mechanisms.
Mitigation strategies for this vulnerability require immediate implementation of stronger random number generation for CAPTCHA components. The ts_random value must be replaced with cryptographically secure random numbers that cannot be predicted or reverse-engineered through date and User-Agent calculations. Web application developers should implement proper entropy sources and ensure that all CAPTCHA-related values are generated using secure random number generators that meet industry standards such as those specified in NIST SP 800-90A. Additionally, the CAPTCHA system should incorporate additional verification factors beyond simple timestamp-based calculations. Organizations should also consider implementing rate limiting and behavioral analysis to detect and prevent automated access patterns. The fix should address the root cause by ensuring that CAPTCHA values are truly random and unpredictable, thereby restoring the intended security controls against automated attacks.