CVE-2006-4273 in vBulletin
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Jelsoft vBulletin 3.5.4 and 3.6.0 allows remote attackers to inject arbitrary web script or HTML by uploading an attachment with a .pdf extension that contains JavaScript, which is processed as script by Microsoft Internet Explorer 6.
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Analysis
by VulDB Data Team • 08/02/2018
The vulnerability described in CVE-2006-4273 represents a critical cross-site scripting flaw affecting Jelsoft vBulletin versions 3.5.4 and 3.6.0. This security weakness enables remote attackers to execute malicious code within the context of other users' browsers through carefully crafted file uploads. The vulnerability specifically exploits the way the forum software handles file attachments, particularly those masquerading as pdf documents but containing embedded javascript code. The attack vector leverages the trust users place in file extensions and the automatic execution behavior of older web browsers, creating a dangerous intersection between file validation and script execution. This flaw demonstrates the inherent risks of relying solely on file extension checks rather than comprehensive content analysis for security validation.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the attachment processing module of the vBulletin software. When users upload files with .pdf extensions, the system fails to properly examine the actual file content, instead trusting the file extension to determine the file type. Microsoft Internet Explorer 6, which was prevalent during this time period, processes pdf files through its built-in pdf viewer plugin that executes embedded javascript code within pdf documents. This creates a scenario where attackers can embed malicious javascript within what appears to be a legitimate pdf file, leading to unauthorized script execution in the victim's browser context. The vulnerability operates at the application layer and falls under the CWE-79 category of Cross-site Scripting, specifically manifesting as stored XSS since the malicious content is persisted in the forum's database and executed whenever other users view the attachment.
The operational impact of this vulnerability extends beyond simple script injection, potentially enabling attackers to perform session hijacking, steal user credentials, redirect victims to malicious websites, or execute arbitrary commands on affected systems. The attack requires minimal user interaction beyond viewing the malicious attachment, making it particularly dangerous in forum environments where users frequently download and view attachments from other members. The widespread use of vBulletin forums and Internet Explorer 6 during this period amplified the potential damage, as many organizations had not yet migrated to newer browser versions that would properly handle such embedded content. This vulnerability also highlights the importance of proper security controls in web applications, as the flaw existed in the core file upload handling functionality rather than being a peripheral security issue.
Mitigation strategies for this vulnerability require multiple layers of defensive measures including immediate patching of affected vBulletin installations to the latest security releases, implementation of comprehensive file content validation rather than relying solely on file extensions, and browser security hardening through the use of modern browser versions with better content isolation. Organizations should also implement strict attachment filtering policies that reject potentially dangerous file types, deploy web application firewalls to detect and block malicious content, and educate users about the risks of downloading and viewing attachments from untrusted sources. The remediation process should include thorough security testing of file upload functionality and regular vulnerability assessments to identify similar flaws in other applications. This vulnerability serves as a critical reminder of the importance of proper input validation and the dangers of trusting file extensions without proper content verification, aligning with ATT&CK technique T1566 for initial access through spearphishing attachments and T1059 for command and scripting interpreter usage.