CVE-2005-4454 in LiveJournal
Summary
by MITRE
Validate-before-filter vulnerability in cleanhtml.pl 1.129 in LiveJournal CVS before Dec 7 2005, when the cleancss option is enabled, allows remote attackers to conduct cross-site scripting (XSS) attacks via a "\" (backslash) within a "javascript" scheme in a style property (such as "javas\cript"), which bypasses the "javascript" check before the "\" is stripped and then rendered in web browsers that allow scripting in style sheets.
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Analysis
by VulDB Data Team • 11/12/2024
The vulnerability described in CVE-2005-4454 represents a critical validate-before-filter security flaw in the LiveJournal content management system's cleanhtml.pl script version 1.129. This issue emerged within the LiveJournal CVS repository prior to December 7 2005 and specifically affects systems utilizing the cleancss option for HTML content sanitization. The vulnerability stems from improper input validation that occurs before filtering mechanisms are applied to user-supplied content, creating a pathway for malicious actors to inject cross-site scripting payloads.
The technical implementation of this vulnerability involves a specific pattern where attackers can bypass the HTML sanitization process by inserting a backslash character within a javascript scheme embedded in a style property. This particular construct allows the malicious code to evade detection mechanisms that would normally filter out dangerous javascript content. The cleancss option, when enabled, processes CSS stylesheets and HTML content, but fails to properly sanitize inputs containing backslash-escaped javascript references. This validate-before-filter pattern creates a fundamental security gap where validation logic is executed before filtering, allowing crafted payloads to slip through undetected.
The operational impact of this vulnerability is significant as it enables remote attackers to execute arbitrary javascript code within the context of users' browsers who view compromised content. This opens the door to session hijacking, credential theft, defacement of user accounts, and redirection to malicious websites. The vulnerability affects all users who interact with content processed through the vulnerable LiveJournal system, making it particularly dangerous given the social networking nature of the platform where users frequently share content with others. The attack vector requires no authentication and can be executed through simple content injection, making it highly exploitable in real-world scenarios.
This vulnerability aligns with CWE-1077, which describes the weakness of validate-before-filter, and corresponds to ATT&CK technique T1059.007 for JavaScript execution. The flaw demonstrates poor input validation practices that violate secure coding principles and represents a classic example of how improper security logic design can create exploitable conditions. Organizations should implement comprehensive input sanitization at multiple layers, ensuring that validation and filtering occur in proper sequence to prevent such issues. The remediation involves updating the cleanhtml.pl script to properly handle backslash escaping in javascript schemes and implementing more robust content filtering mechanisms that validate content after all filtering has been applied. Additionally, the system should employ proper HTML escaping and context-aware sanitization to prevent XSS vulnerabilities in CSS and style attribute processing.