CVE-2018-6172 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-2018-6172 represents a critical security flaw in Google Chrome's URL formatting mechanism that exploited the handling of confusable characters to enable domain spoofing attacks. This issue specifically affected Chrome versions prior to 68.0.3440.75 and demonstrated how seemingly innocuous character encoding could be weaponized to deceive users into believing they were visiting legitimate websites when in fact they were interacting with malicious domains. The vulnerability leveraged internationalized domain names that contained characters from different scripts that visually resembled each other, creating opportunities for attackers to craft deceptive URLs that appeared authentic to the unwary user.
The technical root cause of this vulnerability lies in Chrome's insufficient validation of internationalized domain names during URL display and formatting operations. When processing domain names that contained confusable characters, the browser failed to properly distinguish between visually similar characters from different Unicode character sets. This flaw allowed attackers to register domain names using characters from scripts such as Cyrillic that closely resemble Latin characters, creating domains that would appear identical or nearly identical to legitimate websites when rendered in the browser's address bar. The vulnerability specifically impacted the URL formatter component that handles the display of domain names, making it possible for attackers to craft URLs that would visually mimic trusted domains while actually resolving to different IP addresses or web servers.
The operational impact of CVE-2018-6172 extends beyond simple phishing attacks to encompass a broader range of social engineering and man-in-the-middle attack vectors. Attackers could exploit this vulnerability to create convincing fake websites that would fool users into entering sensitive information such as login credentials, personal data, or financial details. The attack surface was particularly concerning because it targeted the fundamental user interface element that users rely on for website authentication and trust verification. Users would not notice the deception during normal browsing because the browser displayed the spoofed domain names in a manner that appeared legitimate, effectively bypassing traditional security mechanisms that depend on user recognition of domain names. This vulnerability aligns with CWE-1004 which addresses insecure default settings and CWE-74 which covers injection flaws, particularly focusing on the improper handling of input that affects the display and interpretation of web addresses.
The mitigation strategies for this vulnerability required immediate browser updates and implementation of proper IDN handling mechanisms. Google addressed this issue by improving Chrome's URL formatting to properly detect and handle confusable characters in internationalized domain names, implementing stricter validation of domain name components before display, and enhancing the browser's ability to distinguish between similar-looking characters from different Unicode scripts. Organizations should have implemented browser update policies to ensure immediate deployment of Chrome version 68.0.3440.75 or later, which contained the necessary fixes. Additionally, security teams should have considered implementing additional monitoring for suspicious domain registrations and user behavior patterns that might indicate attempts to exploit this vulnerability. This issue relates to ATT&CK technique T1566 which covers spearphishing attacks and T1071.001 which covers application layer protocol usage for command and control communications, as the vulnerability could be leveraged in sophisticated phishing campaigns and credential theft operations.
The broader implications of CVE-2018-6172 highlight the challenges inherent in internationalized domain name security and the complexity of handling Unicode characters in web browsers. This vulnerability demonstrated that even seemingly simple user interface components could contain significant security implications when dealing with international character sets and visual similarity attacks. The fix implemented by Google required careful consideration of Unicode normalization rules and character equivalence handling to ensure that legitimate internationalized domain names continued to function properly while preventing spoofing attacks. This vulnerability serves as a reminder of the importance of considering internationalization and localization aspects in security design and the need for comprehensive testing of user interface elements that handle text input and display operations. The remediation process also emphasized the importance of proactive security measures and rapid response protocols for addressing browser-level vulnerabilities that affect user trust and security.