CVE-2008-0206 in captcha
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in captcha\captcha.php in the Captcha! 2.5d and earlier plugin for WordPress allow remote attackers to inject arbitrary web script or HTML via the (1) captcha_ttffolder, (2) captcha_numchars, (3) captcha_ttfrange, or (4) captcha_secret parameter.
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Analysis
by VulDB Data Team • 09/14/2018
The vulnerability identified as CVE-2008-0206 represents a significant security flaw in captcha implementations that allows attackers to execute cross-site scripting attacks through malicious input fields. This vulnerability specifically affects captcha systems that fail to properly sanitize user input, creating opportunities for attackers to inject malicious scripts that can be executed in the context of legitimate user sessions. The flaw stems from inadequate validation and sanitization of input parameters that are processed by captcha mechanisms, particularly when these systems handle user-submitted data without proper encoding or filtering. Such vulnerabilities are particularly dangerous because they can be exploited to bypass authentication mechanisms, steal session cookies, or redirect users to malicious websites while maintaining the appearance of legitimate system interactions.
The technical implementation of this vulnerability typically occurs when captcha systems receive input from users through web forms or API endpoints without proper sanitization of special characters, script tags, or encoded payloads. Attackers can craft malicious input that includes javascript code or other scripting elements that get processed by the captcha system and subsequently rendered in subsequent page responses. This creates a persistent cross-site scripting vector where the injected scripts execute in the browser context of authenticated users who interact with the vulnerable system. The vulnerability is classified under CWE-79 as Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly encode or escape user-controllable data before it is included in web page output. This weakness allows attackers to inject malicious code that can manipulate web page content, steal sensitive information, or perform unauthorized actions on behalf of users.
The operational impact of CVE-2008-0206 extends beyond simple data theft, as it can enable sophisticated attack chains that leverage the compromised captcha system to facilitate further exploitation. When attackers successfully inject malicious scripts through vulnerable captcha mechanisms, they can potentially capture user credentials, session tokens, or other sensitive information that flows through the system. The vulnerability can also be used to redirect users to phishing sites or to inject malicious advertisements that compromise user systems. The attack surface is particularly broad since captcha systems are commonly used across various web applications including login portals, registration forms, comment sections, and contact forms, making the impact of exploitation widespread. According to ATT&CK framework, this vulnerability maps to T1059.007 for Scripting and T1566.001 for Phishing, as it enables attackers to execute malicious scripts and deliver phishing content through compromised captcha systems. The persistence of such vulnerabilities is enhanced by the fact that captcha systems often serve as trusted interfaces where users expect security, making successful exploitation more likely to go undetected.
Mitigation strategies for CVE-2008-0206 should focus on implementing comprehensive input validation and output encoding mechanisms within captcha systems. Organizations must ensure that all user input is properly sanitized using established encoding techniques such as HTML entity encoding, javascript escaping, and proper input validation that rejects suspicious patterns. The implementation of Content Security Policy headers can provide additional protection against script execution, while regular security testing including dynamic application security testing and manual penetration testing can help identify vulnerable captcha implementations. Security patches should be applied to captcha libraries and frameworks, with particular attention to ensuring that all user-controllable parameters are properly escaped before being rendered in web page output. Additionally, implementing proper session management and monitoring for unusual activities can help detect exploitation attempts, while regular security awareness training for developers can prevent similar vulnerabilities from being introduced during system development phases. The vulnerability highlights the critical importance of treating all user input as potentially malicious and implementing defense-in-depth strategies that protect against multiple attack vectors simultaneously.