CVE-2005-4665 in PunBB
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in PunBB 1.2.6 and earlier allows remote attackers to inject arbitrary web script or HTML via Javascript contained in nested, malformed BBcode url tags.
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Analysis
by VulDB Data Team • 07/07/2021
The CVE-2005-4665 vulnerability represents a critical cross-site scripting flaw discovered in PunBB version 1.2.6 and earlier, demonstrating a significant weakness in web application input validation and output sanitization mechanisms. This vulnerability specifically targets the forum software's handling of BBcode url tags, where nested and malformed structures create opportunities for malicious code injection. The flaw exploits the insufficient filtering of user-generated content, particularly when processing BBcode syntax that should normally be restricted to valid hyperlink formatting. Attackers can craft malicious BBcode sequences containing javascript code within url tag parameters, bypassing standard security measures designed to prevent such injections. The vulnerability resides in the application's text processing pipeline where user input is not adequately sanitized before being rendered back to other users, creating a persistent XSS vector that can compromise user sessions and execute unauthorized commands.
The technical implementation of this vulnerability stems from improper input validation within PunBB's BBcode parser, where nested url tags with malformed structures are not properly escaped or validated before HTML output generation. When a user submits content containing nested BBcode url tags with embedded javascript, the application fails to strip or encode the malicious payload, allowing it to be executed in the context of other users' browsers. This represents a classic stored XSS vulnerability where the malicious code is permanently stored in the application's database and executed whenever affected pages are rendered. The vulnerability is particularly dangerous because BBcode is commonly used in forum environments for formatting posts, making it a natural vector for exploitation. The flaw aligns with CWE-79, which defines Cross-site Scripting vulnerabilities as weaknesses that allow attackers to inject malicious scripts into web applications viewed by other users. This vulnerability specifically demonstrates how improper handling of nested structures in markup parsing can create security gaps that bypass traditional security controls.
The operational impact of CVE-2005-4665 extends beyond simple script execution to encompass potential session hijacking, credential theft, and complete browser compromise of affected users. When malicious javascript executes in a victim's browser context, attackers can steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The vulnerability affects all users of affected PunBB installations, making it particularly dangerous for community forums where users trust the platform's security. Attackers can leverage this vulnerability to create persistent backdoors, harvest user credentials, or manipulate forum content to spread additional malware. The impact is amplified by the fact that forum software typically contains sensitive user information, including private messages, personal details, and potentially administrative credentials. This vulnerability directly maps to ATT&CK technique T1531, which describes the use of malicious code injection to gain access to user sessions and perform unauthorized actions. The attack chain typically involves crafting malicious posts with nested BBcode, uploading them to the forum, and waiting for other users to view the content, making it a stealthy and effective vector for long-term compromise.
Mitigation strategies for CVE-2005-4665 require immediate implementation of proper input sanitization and output encoding mechanisms within the PunBB application. Organizations should upgrade to PunBB versions 1.2.7 or later where this vulnerability has been patched, as the official release includes proper BBcode validation and javascript escaping. The fix typically involves implementing strict BBcode parsing rules that prevent nested url tags from containing executable content, combined with comprehensive HTML encoding of all user-generated content before rendering. Additionally, administrators should implement Content Security Policy headers to limit script execution within forum environments, and consider implementing web application firewalls to detect and block suspicious BBcode patterns. Input validation should be strengthened to reject malformed BBcode structures, while output encoding must ensure that all user content is properly escaped before being displayed in HTML contexts. Security monitoring should include detection of unusual BBcode usage patterns and automated scanning for potentially malicious content. The vulnerability highlights the importance of following secure coding practices, particularly around input validation and output encoding, which are fundamental requirements in secure software development lifecycle processes and align with OWASP Top Ten security controls for preventing XSS vulnerabilities.