CVE-2018-6100 in Chrome
Summary
by MITRE
Incorrect handling of confusable characters in URL Formatter in Google Chrome on macOS prior to 66.0.3359.117 allowed a remote attacker to perform domain spoofing via IDN homographs via a crafted domain name.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/23/2023
The vulnerability identified as CVE-2018-6100 represents a critical security flaw in Google Chrome's handling of internationalized domain names on macOS systems. This issue stems from the browser's URL formatter not properly managing confusable characters that can appear similar to legitimate domain name characters, creating opportunities for sophisticated phishing attacks. The vulnerability specifically affects Chrome versions prior to 66.0.3359.117 on macOS platforms, leaving users exposed to domain spoofing techniques that exploit visual similarities between different character sets.
The technical root cause of this vulnerability lies in the improper implementation of internationalized domain name (IDN) handling within Chrome's URL parsing and display mechanisms. When processing domain names containing characters from different scripts or character sets, the browser fails to adequately distinguish between visually similar characters from different languages. This creates a scenario where an attacker can register a domain name using characters that appear identical or nearly identical to a legitimate domain but belong to different character sets, such as using cyrillic characters that visually resemble latin characters. The flaw occurs in the URL formatter component that processes and displays domain names, allowing maliciously crafted domains to be presented in a manner that deceives users into believing they are visiting legitimate websites.
The operational impact of this vulnerability extends beyond simple phishing attacks to encompass broader security implications for user trust and system integrity. Attackers can exploit this weakness by registering domain names that visually mimic well-known organizations, financial institutions, or government websites, potentially leading to credential theft, financial fraud, or data exfiltration. The vulnerability is particularly dangerous because it operates at the user interface level where visual deception is most effective, making it difficult for users to distinguish between legitimate and malicious sites even when employing security awareness practices. This type of attack directly aligns with the tactics described in the ATT&CK framework under the 'Initial Access' and 'Credential Access' domains, specifically leveraging the 'Phishing' technique with 'Spearphishing Attachment' and 'Spearphishing Link' sub-techniques.
The security implications of CVE-2018-6100 demonstrate a fundamental weakness in web browser security architecture that relates to the Common Weakness Enumeration category 1000, which encompasses issues in input validation and character set handling. This vulnerability highlights the complexity of internationalization and localization in security contexts, where the legitimate need to support multiple character sets creates attack surfaces that must be carefully managed. The flaw represents a classic case of insufficient character normalization and validation in web browser implementations, where the system fails to properly canonicalize or validate domain names before displaying them to users. Organizations and individuals relying on Chrome for web browsing activities were particularly vulnerable to this attack vector, as the browser's default behavior would present the spoofed domains in a manner that appeared authentic to the average user.
Mitigation strategies for this vulnerability required immediate browser updates to version 66.0.3359.117 or later, which implemented proper IDN handling and character validation mechanisms. Security practitioners should have implemented additional protective measures including user education about recognizing potential spoofing attempts, network-level monitoring for suspicious domain registrations, and deployment of web application firewalls that could detect and block known malicious domain patterns. The fix involved implementing proper Unicode normalization and validation of domain names before display, ensuring that visually similar characters from different scripts are properly distinguished and that users receive clear warnings when encountering potentially deceptive domain names. This vulnerability underscored the importance of considering internationalization security implications in software development and highlighted the need for comprehensive testing of character handling mechanisms in security-critical applications.