CVE-2018-6166 in Chrome
Summary
by MITRE
Incorrect handling of confusable characters in URL Formatter in Google Chrome prior to 68.0.3440.75 allowed a remote attacker to perform domain spoofing via IDN homographs via a crafted domain name.
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Analysis
by VulDB Data Team • 06/26/2023
The vulnerability identified as CVE-2018-6166 represents a critical security flaw in Google Chrome's handling of internationalized domain names and character encoding. This issue specifically affects Chrome versions prior to 68.0.3440.75 and exploits the improper processing of confusable characters within URL formatters. The vulnerability stems from Chrome's insufficient validation mechanisms when processing internationalized domain names that contain characters from different scripts or character sets that appear visually similar to ASCII characters. This weakness creates an environment where attackers can craft malicious domain names that visually resemble legitimate websites, enabling deceptive user interactions and potential phishing attacks.
The technical implementation of this vulnerability involves the manipulation of Unicode characters and international domain name (IDN) encoding standards. When Chrome processes domain names containing confusable characters, it fails to properly distinguish between visually similar characters from different Unicode blocks. For instance, Cyrillic characters like 'а' (U+0430) can appear identical to Latin characters like 'a' (U+0061) in certain font contexts. This flaw allows attackers to register domains using these confusable characters, creating URLs that appear legitimate to users while actually directing to malicious endpoints. The vulnerability operates at the application layer and leverages the browser's URL display and parsing mechanisms to deceive users into believing they are visiting trusted websites.
The operational impact of CVE-2018-6166 extends beyond simple visual deception to encompass significant security risks for users and organizations. Attackers can exploit this vulnerability to conduct sophisticated phishing campaigns by creating domains that closely resemble well-known websites such as banks, social media platforms, or corporate portals. Users who are not trained to identify such subtle character differences may inadvertently navigate to malicious sites, potentially exposing sensitive credentials, financial information, or corporate data. The vulnerability particularly affects users who rely on browsers without proper IDN security measures, as the visual similarity of characters makes detection extremely difficult. This issue is especially dangerous in enterprise environments where users may be targeted through spear-phishing attacks designed to bypass traditional security controls.
The security implications of this vulnerability align with several established frameworks including CWE-1004 which addresses insecure coding practices related to character encoding and internationalization. From an ATT&CK framework perspective, this vulnerability maps to techniques involving social engineering and credential access through deceptive web content. Organizations should implement comprehensive browser security updates as the primary mitigation strategy, ensuring all Chrome installations are updated to version 68.0.3440.75 or later. Additional defensive measures include implementing browser security policies that enforce strict IDN handling, deploying user education programs to increase awareness of visual spoofing techniques, and utilizing security tools that can detect and block suspicious domain name patterns. Network-level protections such as DNS filtering and web application firewalls can provide additional layers of defense against exploitation attempts. The vulnerability also highlights the importance of proper input validation and character set handling in web applications, emphasizing the need for robust internationalization practices in software development lifecycle processes.