CVE-2020-6401 in Chrome
Summary
by MITRE
Insufficient validation of untrusted input in Omnibox in Google Chrome prior to 80.0.3987.87 allowed a remote attacker to perform domain spoofing via IDN homographs via a crafted domain name.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/10/2025
The vulnerability identified as CVE-2020-6401 represents a critical security flaw in Google Chrome's Omnibox implementation that existed prior to version 80.0.3987.87. This issue stems from inadequate validation of untrusted input during domain name processing, specifically affecting the browser's address bar functionality where users enter URLs and domain names. The vulnerability operates by exploiting the handling of internationalized domain names with homograph characters, which are Unicode characters that visually resemble standard ASCII characters but have different underlying code points. This particular weakness falls under the CWE-20 category of "Improper Input Validation" and demonstrates how insufficient sanitization of user-provided data can lead to severe security implications.
The technical exploitation of this vulnerability enables remote attackers to craft malicious domain names that appear legitimate but actually resolve to different servers or IP addresses. When a user enters such a crafted domain name into Chrome's Omnibox, the browser displays a visually identical representation to a trusted domain while actually navigating to a malicious endpoint. This domain spoofing technique leverages the visual similarity between Unicode characters from different scripts, particularly those from the latin, cyrillic, and other character sets, where characters like the cyrillic "а" (U+0430) appear identical to the latin "a" (U+0061) in many font displays. The vulnerability specifically targets the rendering and validation logic within Chrome's address bar component, which should have implemented proper Unicode normalization and validation to prevent such deceptive representations from being accepted as valid inputs.
The operational impact of CVE-2020-6401 extends beyond simple phishing attacks, as it undermines the fundamental trust model of web browsing and can facilitate sophisticated social engineering campaigns. Attackers can exploit this vulnerability to create convincing fake websites that appear to be legitimate domains such as banking sites, social media platforms, or corporate portals. The attack surface includes not only direct phishing attempts but also man-in-the-middle scenarios where users might unknowingly navigate to malicious servers while believing they are visiting trusted websites. This vulnerability aligns with ATT&CK technique T1566.001 "Phishing: Spearphishing Attachment" and T1566.002 "Phishing: Spearphishing Link" by enabling attackers to craft deceptive URLs that bypass user security awareness and browser security mechanisms. The risk is particularly elevated for users who rely on visual verification of domain names for security assessment, as the visual deception makes traditional security warnings less effective.
Mitigation strategies for CVE-2020-6401 require both immediate and long-term approaches to address the root cause of insufficient input validation. Users should immediately update to Chrome version 80.0.3987.87 or later, which implements proper Unicode validation and normalization for domain names in the Omnibox. Browser vendors should implement comprehensive input sanitization that includes Unicode normalization, character set validation, and explicit checking for homograph attacks. The recommended security controls include enabling automatic updates, implementing browser security policies that enforce strict domain validation, and deploying network-level protections such as DNS-based filtering and URL reputation services. Organizations should also consider implementing user education programs that emphasize the importance of verifying SSL certificates and URL structure even when visual indicators appear correct. From a compliance perspective, this vulnerability demonstrates the necessity of adhering to security standards such as those outlined in NIST SP 800-128 and ISO/IEC 27001, which require proper input validation and secure coding practices to prevent similar vulnerabilities from being introduced into software systems.