CVE-2022-36020 in html-sanitizer
Summary
by MITRE • 09/13/2022
The typo3/html-sanitizer package is an HTML sanitizer, written in PHP, aiming to provide XSS-safe markup based on explicitly allowed tags, attributes and values. Due to a parsing issue in the upstream package `masterminds/html5`, malicious markup used in a sequence with special HTML comments cannot be filtered and sanitized. This allows for a bypass of the cross-site scripting mechanism of `typo3/html-sanitizer`. This issue has been addressed in versions 1.0.7 and 2.0.16 of the `typo3/html-sanitizer` package. Users are advised to upgrade. There are no known workarounds for this issue.
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Analysis
by VulDB Data Team • 10/16/2022
The CVE-2022-36020 vulnerability affects the typo3/html-sanitizer PHP package, which serves as an HTML sanitization library designed to prevent cross-site scripting attacks by filtering malicious markup. This package operates by maintaining explicit allowlists of permitted HTML tags, attributes, and values, creating a security boundary around web applications that process user-generated content. The vulnerability stems from a parsing inconsistency within the upstream dependency masterminds/html5, which handles the core HTML parsing functionality for the sanitization process. When malicious HTML content is crafted in specific sequences involving special HTML comments, the sanitization logic fails to properly identify and neutralize potentially harmful markup elements.
The technical flaw manifests in how the html-sanitizer package processes certain combinations of HTML comments and malicious tags that exploit parsing gaps in the underlying html5 library. This parsing issue creates a condition where the sanitization algorithm cannot effectively distinguish between legitimate and malicious content, allowing XSS payloads to bypass the intended security controls. The vulnerability specifically impacts the sanitization pipeline when processing sequences containing HTML comments that interact with other markup elements in ways that the parser does not properly handle. This represents a classic case of insufficient input validation and sanitization where the underlying parsing mechanism fails to properly normalize or sanitize malformed HTML structures before they are processed by the security controls.
The operational impact of this vulnerability is significant for any TYPO3 application or web platform that relies on the html-sanitizer package for user input validation and XSS protection. Attackers could potentially inject malicious JavaScript code, HTML content, or other harmful markup elements that would normally be blocked by the sanitization process. This bypass enables unauthorized users to execute XSS attacks against other users of the affected applications, potentially leading to session hijacking, data theft, or further exploitation of the web platform. The vulnerability affects both version 1.0.7 and 2.0.16 of the package, indicating that the parsing issue was present across multiple release branches, making the impact broader than initially anticipated.
Organizations using the affected package should immediately upgrade to versions 1.0.7 or 2.0.16 to remediate this vulnerability, as no effective workarounds exist for this specific parsing issue. The fix addresses the underlying parsing inconsistency in the masterminds/html5 dependency, ensuring that all HTML content is properly normalized and sanitized regardless of comment sequences or special markup combinations. Security practitioners should also conduct comprehensive vulnerability assessments of their TYPO3 installations to identify any potential exploitation attempts or lingering impacts from this vulnerability. This issue aligns with CWE-79 (Cross-site Scripting) and ATT&CK techniques related to code injection and credential access through web application vulnerabilities, emphasizing the critical nature of maintaining up-to-date dependencies and proper input sanitization in web security architectures.