CVE-2022-23499 in TYPO3
Summary
by MITRE • 12/14/2022
HTML sanitizer is written in PHP, aiming to provide XSS-safe markup based on explicitly allowed tags, attributes and values. In versions prior to 1.5.0 or 2.1.1, malicious markup used in a sequence with special HTML CDATA sections cannot be filtered and sanitized due to a parsing issue in the upstream package masterminds/html5. This allows bypassing the cross-site scripting mechanism of typo3/html-sanitizer. The upstream package masterminds/html5 provides HTML raw text elements (`script`, `style`, `noframes`, `noembed` and `iframe`) as DOMText nodes, which were not processed and sanitized further. None of the mentioned elements were defined in the default builder configuration, that's why only custom behaviors, using one of those tag names, were vulnerable to cross-site scripting. This issue has been fixed in versions 1.5.0 and 2.1.1.
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Analysis
by VulDB Data Team • 01/08/2023
The vulnerability identified as CVE-2022-23499 represents a critical cross-site scripting weakness within the typo3/html-sanitizer PHP library, specifically affecting versions prior to 1.5.0 and 2.1.1. This flaw stems from an upstream parsing issue within the masterminds/html5 package, which serves as the foundational HTML parsing component for the sanitization process. The vulnerability occurs when maliciously crafted HTML markup is processed in conjunction with special HTML CDATA sections, creating a scenario where the sanitization mechanism fails to properly filter and sanitize the content. The core technical issue lies in how raw text elements are handled within the HTML parsing pipeline, particularly the treatment of DOMText nodes for elements that should normally be restricted or escaped.
The operational impact of this vulnerability is significant as it allows attackers to bypass the intended security controls of the HTML sanitizer, potentially enabling persistent cross-site scripting attacks against users of applications relying on the affected versions. The vulnerability specifically affects HTML raw text elements including script, style, noframes, noembed, and iframe tags, which are processed as DOMText nodes rather than being properly sanitized. These elements are not included in the default builder configuration of the sanitizer, meaning that only custom configurations utilizing these tag names would be vulnerable. This creates a dangerous scenario where legitimate applications might not be immediately aware of the vulnerability if they don't explicitly use these elements in their custom configurations, while those that do use them become exposed to potential XSS attacks through the parsing bypass mechanism.
The underlying technical flaw manifests through a parsing inconsistency in the masterminds/html5 upstream package where certain HTML elements that should be treated as raw text are not properly processed through the sanitization pipeline. When these elements are encountered in HTML content, they are converted to DOMText nodes without proper escaping or restriction, allowing malicious content to pass through the filter mechanism. This parsing issue directly violates the fundamental security principle of input sanitization, where all potentially dangerous content should be properly escaped or removed regardless of its position within the HTML structure. The vulnerability demonstrates a failure in the security controls at the parsing layer rather than the sanitization layer, making it particularly insidious as it can bypass even properly configured security rules.
Organizations utilizing the typo3/html-sanitizer library should immediately upgrade to versions 1.5.0 or 2.1.1 to address this vulnerability, as the fix resolves the parsing inconsistency in the upstream masterminds/html5 package. The remediation process involves not only updating the library but also reviewing custom configurations that might utilize the vulnerable raw text elements to ensure proper handling. Security practitioners should implement monitoring for any attempts to exploit this vulnerability in their environments, particularly focusing on HTML content that might contain script, style, or iframe tags in unexpected contexts. The vulnerability aligns with CWE-79 (Cross-site Scripting) and represents a specific implementation weakness that could be categorized under ATT&CK technique T1203 (Exploitation for Client Execution) when exploited in web applications. This vulnerability underscores the importance of thorough testing of upstream dependencies and the need for comprehensive security validation of HTML processing libraries, as issues in parsing components can have cascading effects on the entire sanitization mechanism.