CVE-2018-6173 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 • 07/17/2024
The vulnerability identified as CVE-2018-6173 represents a critical security flaw in Google Chrome's URL formatting and display mechanisms that enabled sophisticated domain spoofing attacks through the manipulation of internationalized domain names. This issue specifically affected Chrome versions prior to 68.0.3440.75 and exploited the browser's inadequate handling of confusable characters that appear visually similar but have different Unicode representations. The vulnerability falls under the category of Unicode security issues and can be classified as a CWE-1057 weakness related to improper handling of Unicode characters in user interface elements. Attackers could craft domain names using characters from different scripts that visually resemble legitimate domains, creating deceptive URLs that would appear authentic to users while directing them to malicious destinations.
The technical implementation of this vulnerability stems from Chrome's URL formatter not properly implementing Unicode bidirectional algorithm handling and confusable character detection when displaying internationalized domain names. When users encountered URLs containing homograph characters from different Unicode scripts, the browser would display them in a way that made the malicious domain appear identical or nearly identical to a legitimate one. This occurred because the browser's display logic failed to properly normalize or flag potentially deceptive Unicode sequences, allowing attackers to register domains using characters from scripts like Arabic, Cyrillic, or other Unicode blocks that visually mimic Latin characters. The flaw essentially created a bypass for standard security mechanisms that rely on visual domain recognition, making it particularly dangerous for phishing attacks targeting users who might not notice subtle visual differences in domain names.
The operational impact of this vulnerability extends beyond simple phishing attempts to encompass broader security implications for user trust and browser security models. Users could be deceived into believing they were visiting legitimate websites while actually navigating to attacker-controlled domains, potentially exposing sensitive information, credentials, or financial data. The vulnerability particularly affected high-value targets including financial institutions, government agencies, and large corporations whose domain names might be targeted for homograph attacks. Security researchers have noted that this type of attack can bypass traditional security controls like SSL certificate validation, as users often focus on visual domain appearance rather than technical certificate details. The attack vector required minimal user interaction beyond visiting a maliciously crafted URL, making it particularly effective for social engineering campaigns. This vulnerability directly relates to ATT&CK technique T1566.001 which involves phishing with malicious attachments or links, and T1562.001 which encompasses the use of web proxies or malicious websites to evade detection.
Mitigation strategies for CVE-2018-6173 required immediate browser updates to Chrome version 68.0.3440.75 or later, which implemented proper Unicode normalization and confusable character detection in URL display logic. Organizations should have deployed these updates immediately and conducted user awareness training to help identify potentially deceptive URLs. Additional protective measures included implementing browser security policies that enforced stricter URL validation, deploying web filtering solutions that could detect and block suspicious domain patterns, and establishing monitoring procedures to identify attempts at registering or using homograph domains. The fix implemented by Google involved enhanced Unicode handling that properly identifies and displays potentially deceptive characters while maintaining compatibility with legitimate internationalized domain names. This vulnerability highlighted the importance of proper Unicode security implementation in web browsers and led to improved security standards for internationalized domain name handling across the industry. Organizations should have also reviewed their incident response procedures to ensure rapid identification and remediation of similar Unicode-based security issues.