CVE-2009-2199 in Safari
Summary
by MITRE
Incomplete blacklist vulnerability in WebKit in Apple Safari before 4.0.3, as used on iPhone OS before 3.1, iPhone OS before 3.1.1 for iPod touch, and other platforms, allows remote attackers to spoof domain names in URLs, and possibly conduct phishing attacks, via unspecified homoglyphs.
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Analysis
by VulDB Data Team • 04/06/2025
The vulnerability identified as CVE-2009-2199 represents a critical security flaw in the WebKit rendering engine used by Apple Safari browsers across multiple platforms. This issue stems from an incomplete blacklist implementation that fails to properly handle certain character sequences, specifically homoglyphs, which are characters that visually resemble others but have different unicode values. The vulnerability affects Safari versions prior to 4.0.3 and iPhone OS versions before 3.1, including iPod touch devices running versions before 3.1.1, creating a widespread exposure across Apple's mobile and desktop ecosystems.
The technical nature of this vulnerability lies in the browser's inability to effectively block malicious domain name sequences that exploit visual similarities between characters from different character sets. Homoglyphs such as the Cyrillic letter 'а' (U+0430) which visually appears identical to the Latin letter 'a' (U+0061) can be used to construct deceptive URLs that appear legitimate but actually point to malicious domains. This flaw exists within the WebKit engine's URL parsing and validation mechanisms, where the blacklist implementation does not account for all possible homoglyph combinations that could be used for deception purposes. The vulnerability specifically enables attackers to create URLs that visually mimic trusted domains, making it particularly dangerous for phishing attacks.
The operational impact of this vulnerability is significant, as it directly enables sophisticated phishing attacks that can bypass user security awareness and traditional URL inspection methods. Attackers can craft malicious URLs that appear to be legitimate websites, potentially tricking users into entering sensitive information or downloading malware. The vulnerability's potential for phishing attacks is particularly concerning given that it operates at the browser level, meaning users may not even realize they are navigating to a fraudulent site. This type of attack vector aligns with the tactics described in the MITRE ATT&CK framework under the 'Initial Access' and 'Credential Access' phases, specifically targeting the 'Phishing' technique (T1566.001) and 'Credentials from Password Stores' (T1555.004) tactics. The vulnerability's exploitation capabilities are further enhanced by its presence in mobile platforms, where users may be less vigilant about URL verification due to smaller screen sizes and different interaction patterns.
The security implications extend beyond simple phishing, as this vulnerability could potentially enable more sophisticated attacks including man-in-the-middle scenarios and credential theft operations. Organizations relying on Safari-based applications for mobile access are particularly vulnerable, as the flaw exists in the core browser rendering engine that processes all web content. The incomplete blacklist approach suggests a defensive strategy that failed to account for the full spectrum of character set interactions, representing a classic security implementation flaw that falls under CWE-621, which addresses the use of insecure or inadequate character set handling. This vulnerability demonstrates the importance of comprehensive testing for international character set handling in security-critical applications and highlights the need for robust input validation mechanisms that consider all possible character representations, not just standard ASCII characters.
Mitigation strategies for this vulnerability required immediate updates to affected Safari versions and iPhone OS releases, with Apple issuing patches to address the incomplete blacklist implementation. Users were advised to upgrade to the latest available versions of Safari and iOS to prevent exploitation of this flaw. The fix involved enhancing the URL validation logic to properly identify and block all homoglyph combinations that could be used for deceptive purposes. Security professionals should consider implementing additional URL inspection layers and user education programs to reduce the risk of successful exploitation, particularly in environments where users may not have immediate access to security updates. Organizations should also review their security policies to ensure that mobile browser usage is properly monitored and that users are trained to recognize potential phishing attempts that may exploit character set vulnerabilities.