CVE-2022-28367 in AntiSamy
Summary
by MITRE • 04/22/2022
OWASP AntiSamy before 1.6.6 allows XSS via HTML tag smuggling on STYLE content with crafted input. The output serializer does not properly encode the supposed Cascading Style Sheets (CSS) content.
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Analysis
by VulDB Data Team • 04/28/2022
The vulnerability identified as CVE-2022-28367 affects the OWASP AntiSamy library version 1.6.5 and earlier, representing a critical cross-site scripting weakness that exploits HTML tag smuggling techniques within STYLE content. This flaw resides in the output serializer component of the library which fails to properly encode CSS content that is processed through HTML tags, creating a pathway for malicious actors to bypass security controls designed to prevent XSS attacks. The vulnerability specifically targets the handling of CSS content within STYLE elements, where crafted input can manipulate the serialization process to inject malicious scripts that would otherwise be blocked by standard sanitization mechanisms.
The technical implementation of this vulnerability stems from insufficient sanitization of CSS content within HTML STYLE tags, where the AntiSamy library's output serializer does not adequately escape or encode CSS properties and values that might contain executable code. Attackers can craft malicious input that appears to be legitimate CSS content but contains embedded JavaScript or other malicious payloads that are not properly neutralized during the serialization process. This creates a scenario where the library's security controls fail to distinguish between safe CSS content and potentially harmful script injection attempts, particularly when dealing with complex CSS features that allow for advanced styling capabilities including expression functions and other potentially dangerous CSS properties.
The operational impact of this vulnerability extends beyond simple XSS exploitation, as it undermines the fundamental security assumptions of the AntiSamy library which is widely deployed in web applications for HTML sanitization and XSS protection. Organizations relying on affected versions of OWASP AntiSamy may experience unauthorized code execution, session hijacking, data theft, and other malicious activities that can compromise entire web applications. The vulnerability particularly affects applications that process user-generated content through the AntiSamy library, making it a significant concern for content management systems, forums, comment systems, and any platform that accepts HTML input from untrusted sources. The exploitation mechanism leverages the library's handling of CSS content within STYLE tags, where the lack of proper encoding allows malicious CSS to be transformed into executable JavaScript during the output rendering phase.
This vulnerability aligns with CWE-79 which describes Cross-Site Scripting flaws in the context of improper encoding or sanitization of user input. The attack vector can be mapped to ATT&CK technique T1059.007 which covers JavaScript and VBScript, as the vulnerability enables execution of malicious scripts through CSS content. Additionally, the issue demonstrates characteristics of T1566 which covers credential access through social engineering, as the bypass of security controls can lead to unauthorized access to user sessions and data. Organizations should implement immediate mitigations including upgrading to AntiSamy version 1.6.6 or later, which includes proper CSS content encoding and sanitization. Additional protective measures such as Content Security Policy headers, input validation at multiple layers, and regular security testing of HTML sanitization components should be implemented to reduce risk exposure. The vulnerability highlights the importance of comprehensive security testing for HTML sanitization libraries and demonstrates how seemingly benign CSS processing can become a vector for sophisticated attacks.
The remediation approach requires not only updating to the patched version of OWASP AntiSamy but also implementing additional defensive measures such as runtime monitoring for unusual CSS processing patterns, enhanced input validation, and regular security audits of HTML sanitization components. Organizations should also consider implementing web application firewalls and additional security layers to protect against similar vulnerabilities in other components of their security infrastructure. The vulnerability serves as a reminder of the complexity involved in HTML sanitization and the need for thorough testing of security controls in web applications.