CVE-2008-1502 in Moodle
Summary
by MITRE
The _bad_protocol_once function in phpgwapi/inc/class.kses.inc.php in KSES, as used in eGroupWare before 1.4.003, Moodle before 1.8.5, and other products, allows remote attackers to bypass HTML filtering and conduct cross-site scripting (XSS) attacks via a string containing crafted URL protocols.
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Analysis
by VulDB Data Team • 04/23/2025
The vulnerability identified as CVE-2008-1502 represents a critical flaw in HTML sanitization mechanisms within the KSES library, which is widely deployed across various web applications including eGroupWare and Moodle. This security issue stems from improper handling of URL protocols during HTML content filtering, creating an avenue for malicious actors to circumvent protective measures designed to prevent cross-site scripting attacks. The vulnerability specifically affects versions of KSES prior to 1.4.003 in eGroupWare and Moodle versions before 1.8.5, indicating a widespread impact across multiple platforms that rely on this filtering component.
The technical implementation of this vulnerability resides in the _bad_protocol_once function within the phpgwapi/inc/class.kses.inc.php file, where the system fails to adequately validate or sanitize URL protocols contained within user-supplied input. This function is responsible for processing and filtering HTML content to remove potentially dangerous elements while preserving legitimate markup. However, the flaw allows attackers to craft strings containing specially formatted URL protocols that bypass the intended filtering logic, enabling the insertion of malicious script tags or other harmful HTML content. The vulnerability operates through protocol-based bypass techniques where the system does not properly distinguish between safe and dangerous protocol schemes, particularly when dealing with edge cases or unconventional protocol specifications.
The operational impact of this vulnerability is severe as it directly enables remote code execution through cross-site scripting attacks, allowing malicious users to inject arbitrary JavaScript code into web pages viewed by other users. This capability can lead to session hijacking, data theft, defacement of web applications, and potential privilege escalation within affected systems. The vulnerability's exploitation does not require authentication, making it particularly dangerous as it can be leveraged by attackers without prior access credentials. The implications extend beyond simple XSS attacks since successful exploitation can compromise entire user sessions and potentially provide attackers with elevated privileges within the vulnerable applications.
Security professionals should address this vulnerability by implementing immediate patches and updates to affected versions of KSES, eGroupWare, and Moodle. The mitigation strategy should include thorough code review of all HTML sanitization functions, implementation of more robust protocol validation mechanisms, and deployment of additional security layers such as Content Security Policy headers. Organizations should also consider implementing web application firewalls and input validation controls to provide defense-in-depth measures. This vulnerability aligns with CWE-79 which categorizes improper neutralization of input during web page generation, and maps to ATT&CK technique T1165 for "Unvalidated Input" and T1059.007 for "Command and Scripting Interpreter: JavaScript" within the attack framework. The remediation process should also include comprehensive testing of all input sanitization components to ensure that similar vulnerabilities do not exist in other parts of the application stack.