CVE-2006-0063 in phpBB
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in phpBB 2.0.19, when "Allowed HTML tags" is enabled, allows remote attackers to inject arbitrary web script or HTML via a permitted HTML tag with (single quote) characters and active attributes such as onmouseover, a variant of CVE-2005-4357.
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Analysis
by VulDB Data Team • 07/17/2018
The vulnerability described in CVE-2006-0063 represents a critical cross-site scripting flaw within the phpBB forum software version 2.0.19. This security weakness specifically manifests when the "Allowed HTML tags" feature is enabled, creating an exploitable condition that permits remote attackers to inject malicious web scripts or HTML content into forum posts. The vulnerability operates by leveraging permitted HTML tags that contain single quote characters alongside active attributes such as onmouseover, which serves as a direct variant of the previously identified CVE-2005-4357 vulnerability. The flaw resides in the software's insufficient input validation and output encoding mechanisms, particularly when processing user-generated content that contains HTML markup.
The technical implementation of this XSS vulnerability stems from phpBB's failure to properly sanitize or escape user input that contains HTML tags with event handlers. When administrators enable the "Allowed HTML tags" functionality, they expect to permit safe HTML elements such as bold, italic, or links while maintaining security. However, the system does not adequately filter or encode attributes that trigger JavaScript execution when the HTML is rendered in web browsers. The specific exploitation vector involves crafting malicious HTML content that includes single quotes within attribute values, which when processed through the vulnerable phpBB version, can execute arbitrary JavaScript code in the context of other users' browsers. This particular variant demonstrates how seemingly innocuous HTML attributes like onmouseover can become dangerous when combined with improperly sanitized user input.
The operational impact of CVE-2006-0063 extends beyond simple script injection, as it can enable attackers to perform various malicious activities through compromised forum sessions. An attacker could exploit this vulnerability to steal session cookies, redirect users to malicious websites, deface forum content, or even execute more sophisticated attacks such as credential harvesting or browser-based malware delivery. The vulnerability affects all users who view forum posts containing the maliciously crafted HTML, making it particularly dangerous for widely accessible forums where many users might be logged in with administrative privileges. The attack requires no special privileges from the attacker beyond the ability to post content to the forum, making it an accessible threat for anyone with basic forum account access. This vulnerability essentially transforms any forum user into a potential vector for distributing malicious content throughout the entire user base.
Mitigation strategies for this vulnerability should focus on immediate patching of the phpBB software to version 2.0.20 or later, which contains the necessary security fixes. Organizations should also implement comprehensive input validation and output encoding mechanisms, ensuring that all user-generated content is properly sanitized before being stored or displayed. The recommended approach includes disabling the "Allowed HTML tags" feature entirely unless absolutely necessary, as this functionality inherently introduces security risks. Additionally, implementing Content Security Policy headers can provide an additional layer of protection against XSS attacks by restricting the sources from which scripts can be loaded. Security monitoring should be enhanced to detect unusual posting patterns or content that might indicate exploitation attempts, while regular security audits should verify that no other similar vulnerabilities exist within the forum software or related systems. This vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws, and represents a clear example of how HTML sanitization failures can lead to severe security consequences in web applications. The ATT&CK framework categorizes this as a web application vulnerability exploitation technique that falls under the broader category of code injection attacks, where the attacker leverages legitimate application functionality to execute malicious code in victim browsers.