CVE-2009-0404 in htmLawed
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in Bioinformatics htmLawed 1.1.3 and 1.1.4 allow remote attackers to inject arbitrary web script or HTML via invalid Cascading Style Sheets (CSS) expressions in the style attribute, which is processed by Internet Explorer 7.
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Analysis
by VulDB Data Team • 10/27/2018
The vulnerability identified as CVE-2009-0404 represents a critical cross-site scripting flaw affecting the htmLawed library version 1.1.3 and 1.1.4 used in bioinformatics applications. This security weakness stems from inadequate input validation mechanisms within the library's processing of HTML content, specifically when handling CSS style attributes. The flaw manifests when malicious actors inject malformed CSS expressions into the style attribute of HTML elements, exploiting the way Internet Explorer 7 processes these invalid CSS constructs. The vulnerability is particularly dangerous because it leverages the browser's native CSS parsing behavior rather than relying on traditional HTML injection vectors, making detection and prevention more challenging for security systems. This issue affects web applications that utilize htmLawed for sanitizing user input, creating a pathway for attackers to execute malicious scripts in the context of a victim's browser session.
The technical implementation of this vulnerability exploits the specific parsing characteristics of Internet Explorer 7's CSS engine, which processes certain invalid CSS expressions in ways that can trigger script execution. When htmLawed processes HTML content containing malicious CSS expressions within style attributes, the library fails to properly sanitize these constructs before rendering them in the browser. The flaw occurs because the library does not adequately validate or strip CSS expressions that could be interpreted by IE7 as executable code, particularly when these expressions contain javascript: protocols or other malicious payloads. This represents a classic case of improper input validation and output encoding, where the system assumes that CSS expressions are safe without proper sanitization. The vulnerability is categorized under CWE-79 as Improper Neutralization of Input During Web Page Generation, which directly relates to the failure to properly escape or validate user-controllable input before it reaches the browser rendering engine.
The operational impact of CVE-2009-0404 extends beyond simple script injection, creating potential for session hijacking, credential theft, and full browser compromise when exploited against authenticated users. Attackers can craft malicious CSS expressions that execute in the context of a victim's browsing session, potentially stealing cookies, session tokens, or other sensitive information. The vulnerability affects web applications that process user-generated content, particularly in bioinformatics environments where researchers may input data containing malformed CSS expressions. Since the flaw is specific to Internet Explorer 7, it creates a targeted attack vector that requires no complex exploitation techniques beyond crafting the appropriate CSS payload. The vulnerability also demonstrates how seemingly benign HTML attributes can become attack vectors when processed by specific browser implementations, highlighting the importance of considering browser-specific behaviors during security assessments.
Mitigation strategies for CVE-2009-0404 should focus on immediate library updates and input validation improvements. Organizations should upgrade to newer versions of htmLawed that properly address CSS expression sanitization and implement comprehensive input validation at multiple layers of their applications. The recommended approach includes implementing strict CSS validation rules that reject or sanitize CSS expressions containing executable code patterns, particularly those that could trigger IE7-specific behaviors. Security teams should also consider implementing Content Security Policy headers to limit script execution capabilities, though this is a secondary defense mechanism. Organizations using affected versions should conduct thorough code reviews to identify all instances where htmLawed is utilized for processing user input, ensuring that all style attribute processing is properly sanitized. The vulnerability underscores the importance of maintaining up-to-date security libraries and implementing defense-in-depth strategies that protect against multiple attack vectors. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 for Scripting and T1531 for Account Access, as it enables attackers to execute malicious scripts and potentially gain unauthorized access to user accounts through session hijacking techniques.