CVE-2018-1000643 in AntiSamy
Summary
by MITRE
OWASP OWASP ANTISAMY version 1.5.7 and earlier contains a Cross Site Scripting (XSS) vulnerability in AntiSamy.scan() - for both SAX & DOM that can result in Cross Site Scripting.
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Analysis
by VulDB Data Team • 05/02/2023
The vulnerability identified as CVE-2018-1000643 represents a critical cross site scripting weakness within the OWASP AntiSamy library version 1.5.7 and earlier. This security flaw specifically affects the AntiSamy.scan() method implementation when processing both SAX and DOM parsers, creating an avenue for malicious actors to inject harmful scripts into web applications that utilize this library for HTML sanitization. The vulnerability stems from insufficient input validation and output encoding mechanisms within the library's core processing functions, which fail to properly neutralize potentially dangerous markup sequences that could be executed in victim browsers.
The technical exploitation of this vulnerability occurs when the AntiSamy.scan() method processes user-supplied HTML content through either SAX or DOM parsing mechanisms. The flaw allows attackers to craft malicious input that bypasses the library's intended sanitization logic, enabling the execution of arbitrary JavaScript code within the context of legitimate web applications. This occurs because the library's parsing routines do not adequately sanitize or escape special characters and markup sequences that could be interpreted as executable code by web browsers. The vulnerability manifests when the library processes HTML fragments containing script tags, event handlers, or other malicious constructs that should be neutralized during the sanitization process but are instead passed through to the output.
From an operational impact perspective, this vulnerability poses significant risks to web applications that depend on AntiSamy for HTML sanitization and content filtering. Attackers could leverage this weakness to perform session hijacking, defacement of web pages, data theft, or redirection to malicious sites. The vulnerability affects applications across various industries including e-commerce platforms, content management systems, and social media applications where user-generated content is processed. The exploitation requires minimal technical skill and can be automated, making it particularly dangerous for widespread deployment. Organizations using affected versions may experience unauthorized access to sensitive user data, compromise of user sessions, and potential system-wide infiltration through the executed malicious scripts.
The vulnerability aligns with CWE-79 which categorizes cross site scripting flaws as weaknesses in input validation and output encoding, and maps to ATT&CK technique T1203 which covers exploitation of web application vulnerabilities for code execution. The flaw specifically relates to the improper handling of user-supplied input during the HTML sanitization process, where the library fails to properly distinguish between legitimate content and malicious markup. Organizations should immediately upgrade to AntiSamy version 1.5.8 or later, which includes patches addressing the sanitization bypass. Additional mitigations include implementing strict content security policies, deploying web application firewalls, and conducting thorough code reviews to identify other potential injection points. The vulnerability demonstrates the critical importance of proper input validation and output encoding in security libraries, particularly those handling user-generated content in web applications.