CVE-2007-3742 in Safari
Summary
by MITRE
WebKit in Apple Safari 3 Beta before Update 3.0.3, and iPhone before 1.0.1, does not properly handle the interaction between International Domain Name (IDN) support and Unicode fonts, which allows remote attackers to create a URL containing "look-alike characters" (homographs) and possibly perform phishing attacks.
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Analysis
by VulDB Data Team • 07/23/2019
The vulnerability described in CVE-2007-3742 represents a critical security flaw in Apple Safari's WebKit rendering engine that exploited the intersection of International Domain Name support and Unicode font handling. This issue affected Safari 3 Beta versions prior to Update 3.0.3 and iPhone operating systems before version 1.0.1, creating a significant attack surface for malicious actors seeking to exploit user trust through deceptive web navigation. The flaw stemmed from how the browser processed domain names containing characters from different Unicode scripts that visually resemble each other, particularly affecting the handling of internationalized domain names where legitimate domains could be visually indistinguishable from malicious counterparts.
The technical implementation of this vulnerability involved WebKit's insufficient validation of domain name character sets when displaying URLs in the browser's address bar and navigation elements. When users encountered websites with International Domain Names, the browser would render domain labels using Unicode fonts that contained characters from different scripts, such as Latin, Cyrillic, or Arabic characters, which could appear identical or nearly identical to the human eye. This occurred because the browser's URL parsing and display logic did not properly distinguish between visually similar characters from different Unicode blocks, allowing attackers to register domain names using homograph characters that looked authentic to unsuspecting users. The vulnerability specifically manifested when the browser displayed these domains in the address bar without adequate visual distinction between legitimate and malicious character sets.
The operational impact of this vulnerability was severe and directly enabled sophisticated phishing attacks that could deceive users into trusting malicious websites. Attackers could register domain names using visually identical characters from different Unicode scripts, such as using Cyrillic characters that look like Latin letters, making it appear as though they were visiting legitimate websites like "paypal.com" when they were actually visiting "pаypal.com" where the 'a' character was actually a Cyrillic character. This created an environment where users might unknowingly enter sensitive information on fraudulent websites, believing they were interacting with trusted entities. The vulnerability was particularly dangerous because it bypassed traditional security mechanisms such as SSL certificate validation, as users were deceived by the visual similarity of the URLs rather than technical certificate issues. This attack vector represented a significant threat to user security and trust in web navigation, as it exploited human cognitive limitations in distinguishing between similar-looking characters.
The implications of this vulnerability align with CWE-1004, which describes Insufficient User Input Validation, and specifically relates to CWE-20, which covers Improper Input Validation. The attack pattern corresponds to techniques found in the ATT&CK framework under T1566, which covers Phishing, and T1071.004, which involves Application Layer Protocol: DNS. The vulnerability demonstrated how font rendering and character set handling could create security risks beyond traditional input validation concerns, requiring browsers to implement more sophisticated Unicode normalization and display logic. This flaw highlighted the importance of considering internationalization aspects in security design and led to improved practices in how web browsers handle internationalized domain names and character set display.
Mitigation strategies for this vulnerability required both immediate updates to affected Safari versions and broader improvements to browser security architecture. Users needed to update to Safari 3.0.3 or later versions that included proper Unicode handling and domain name validation. Browser vendors subsequently implemented more robust internationalized domain name support that either displayed domain names in a standardized format or provided clear visual indicators when using non-Latin character sets. The solution involved enhancing the URL display logic to prevent visual homograph attacks, typically through mechanisms that either normalize domain names to ASCII equivalents or provide explicit warnings when non-standard character sets are detected. Organizations implementing security policies needed to educate users about the risks of visual phishing attacks and the importance of verifying SSL certificates regardless of URL appearance, while browser developers incorporated more sophisticated character set validation into their rendering engines to prevent similar vulnerabilities from emerging in the future.