CVE-2009-0153 in Mac OS X
Summary
by MITRE
International Components for Unicode (ICU) 4.0, 3.6, and other 3.x versions, as used in Apple Mac OS X 10.5 before 10.5.7, iPhone OS 1.0 through 2.2.1, iPhone OS for iPod touch 1.1 through 2.2.1, Fedora 9 and 10, and possibly other operating systems, does not properly handle invalid byte sequences during Unicode conversion, which might allow remote attackers to conduct cross-site scripting (XSS) attacks.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/04/2019
The vulnerability identified as CVE-2009-0153 resides within the International Components for Unicode (ICU) library version 4.0, 3.6, and other 3.x releases that are integrated into several major operating systems including Apple Mac OS X, iPhone OS, and Fedora distributions. This flaw represents a critical security issue that stems from improper handling of invalid byte sequences during Unicode conversion processes, creating a pathway for malicious actors to exploit cross-site scripting vulnerabilities. The vulnerability affects systems that rely on ICU for internationalization and Unicode processing, making it particularly dangerous in web environments where user input is processed and displayed.
The technical root cause of this vulnerability lies in the ICU library's insufficient validation mechanisms when processing malformed Unicode byte sequences. When the library encounters invalid byte patterns during conversion operations, it fails to properly sanitize or reject these sequences, allowing them to propagate through the system. This behavior creates a condition where attackers can craft malicious input containing specially constructed invalid Unicode sequences that, when processed by applications using ICU, can bypass normal security controls. The flaw specifically manifests during character encoding conversion processes where the library does not adequately check for valid Unicode byte patterns, leading to potential code injection scenarios.
The operational impact of this vulnerability extends across multiple platforms and applications that utilize the affected ICU versions, making it particularly dangerous in web environments where user-supplied data is processed. Attackers can exploit this weakness to inject malicious scripts into web pages, potentially leading to session hijacking, data theft, or unauthorized access to user accounts. The vulnerability is especially concerning because it affects widely deployed systems including Apple's mobile and desktop operating systems, as well as Linux distributions, creating a broad attack surface. Applications that process user input through ICU for Unicode handling become vulnerable to XSS attacks, as the invalid byte sequences can be interpreted as executable code by web browsers or application frameworks.
Mitigation strategies for this vulnerability require immediate patching of affected ICU library versions, with system administrators prioritizing updates to ICU 4.1 or later versions that contain proper validation mechanisms. Organizations should implement input sanitization measures at multiple layers, including web application firewalls and application-level validation, to provide defense-in-depth against potential exploitation attempts. The vulnerability aligns with CWE-170, which describes improper handling of Unicode sequences, and maps to ATT&CK technique T1203, involving exploitation of input validation weaknesses. System administrators should also consider implementing monitoring for unusual Unicode processing patterns and regularly review application logs for signs of attempted exploitation. Additionally, developers should ensure that all user input is properly validated and sanitized before processing through any Unicode conversion functions, particularly in web applications where XSS vulnerabilities are most commonly exploited.