XSS Filter Bypass in Joomla Core via HTML Data URIs

Executive Summary

This vulnerability is a Cross-Site Scripting (XSS) flaw in Joomla! Core versions 1.5.0-5.4.8 and 6.0.0-6.1.3. It involves bypassing the XSS filter by injecting whitespace characters into HTML data URIs. The cleanAttribute method fails to remove these malicious inputs, allowing an XSS attack vector.

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Detection Guidance

This vulnerability involves an XSS filter bypass in Joomla's InputFilter via whitespace characters in HTML data URIs. To detect it, inspect Joomla installations for versions 1.5.0-5.4.8 or 6.0.0-6.1.3. Check for unusual whitespace patterns in HTML data URIs or unexpected script execution in user inputs.

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Impact Analysis

An attacker could exploit this to inject malicious scripts into web pages viewed by users. This may lead to theft of session cookies, credentials, or other sensitive data. Users with high privileges are particularly at risk if the attack targets admin interfaces.

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Compliance Impact

This XSS vulnerability could lead to unauthorized access to personal data, violating GDPR's integrity and confidentiality principles. For HIPAA, it may expose protected health information, risking compliance with security requirements. Organizations must patch to avoid regulatory penalties.

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Mitigation Strategies

Immediately update Joomla to the latest patched version to address the XSS filter bypass. If updating is not possible, apply Joomla's official security patches or disable HTML data URI handling in the InputFilter configuration. Monitor for any signs of exploitation or unusual activity.

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