CVE-2018-6107 in Chrome
Summary
by MITRE
Incorrect handling of confusable characters in URL Formatter in Google Chrome prior to 66.0.3359.106 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 • 07/19/2024
The vulnerability identified as CVE-2018-6107 represents a critical security flaw in Google Chrome's URL formatting mechanism that exploited the handling of confusable characters in internationalized domain names. This issue specifically affected Chrome versions prior to 66.0.3359.106 and enabled remote attackers to conduct domain spoofing attacks through the manipulation of internationalized domain name homographs. The vulnerability stems from Chrome's inadequate processing of Unicode characters that appear visually similar but have different underlying code points, creating opportunities for malicious actors to craft deceptive domain names that mimic legitimate websites.
The technical flaw resides in Chrome's URL formatter's insufficient validation of confusable Unicode characters within domain names. When processing internationalized domain names, the browser failed to properly distinguish between visually identical or similar characters from different Unicode scripts, allowing attackers to register domains using characters that look identical to ASCII characters but have different code points. This creates a scenario where a user might see a URL that appears to be a legitimate website such as "https://www.example.com" but is actually pointing to a malicious domain using confusable characters that are visually indistinguishable from the original. The vulnerability specifically impacts the display and parsing of Internationalized Domain Names in Applications protocol which governs how domain names containing non-ASCII characters should be handled.
The operational impact of this vulnerability extends beyond simple phishing attacks to encompass a broader range of social engineering and man-in-the-middle attack vectors. Attackers could exploit this flaw to create malicious websites that appear legitimate to users who might not notice the subtle character differences in the URL bar. This type of attack is particularly dangerous because it bypasses traditional security measures such as SSL certificate validation, as the underlying security certificates are still valid for the malicious domain. Users are often deceived into trusting these sites due to the visual similarity to legitimate domains, potentially leading to credential theft, financial fraud, or malware distribution. The vulnerability aligns with CWE-1004 which addresses insecure default permissions and improper handling of character encoding in web applications, and maps to ATT&CK technique T1071.004 for application layer protocol tunneling and T1566 for phishing attacks.
Mitigation strategies for this vulnerability require a multi-layered approach that includes immediate software updates to the patched Chrome version, implementation of additional URL validation mechanisms, and enhanced user awareness training. Organizations should ensure all Chrome installations are updated to version 66.0.3359.106 or later where the fix has been implemented. The fix involves improved handling of confusable Unicode characters through the implementation of more robust character validation and display mechanisms that either prevent the use of visually confusable characters or properly display them to users. Additional mitigations include implementing browser security policies that enforce stricter URL validation, deploying web application firewalls that can detect and block suspicious domain name patterns, and establishing user education programs that highlight the importance of carefully examining URLs for potential character manipulation. Security teams should also consider implementing monitoring systems that can detect unusual domain name registration patterns or attempts to register domains with confusable character sequences. The vulnerability demonstrates the critical importance of proper internationalization handling in web browsers and highlights the need for continuous security testing of character encoding and display mechanisms.