CVE-2021-21215 in Chrome
Summary
by MITRE • 04/26/2021
Inappropriate implementation in Autofill in Google Chrome prior to 90.0.4430.72 allowed a remote attacker to spoof security UI via a crafted HTML page.
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Analysis
by VulDB Data Team • 04/30/2021
The vulnerability identified as CVE-2021-21215 represents a critical flaw in Google Chrome's Autofill implementation that undermines the browser's security user interface mechanisms. This weakness exists in versions prior to 90.0.4430.72 and enables remote attackers to manipulate the browser's security warnings and notifications through carefully constructed HTML content. The issue stems from an improper handling of security UI elements within the Autofill feature, which is designed to assist users in filling out forms automatically while maintaining security boundaries. When exploited, this vulnerability allows attackers to present misleading security warnings or hide legitimate security prompts, potentially deceiving users into making unsafe decisions during web interactions.
The technical implementation flaw resides in how Chrome's Autofill component processes and displays security notifications when users interact with web forms. Specifically, the vulnerability occurs when the browser fails to properly validate or sanitize HTML content that attempts to manipulate the security UI elements associated with form filling operations. This improper validation creates an attack surface where malicious actors can inject crafted HTML sequences that override or spoof the browser's legitimate security warnings. The flaw is particularly concerning because it directly impacts the browser's ability to protect users from phishing attempts, credential theft, and other web-based attacks that rely on security UI deception. According to CWE classification, this vulnerability maps to CWE-611 Improper Restriction of XML External Entity Reference, as it involves improper handling of external content that affects security-sensitive UI elements. The attack vector requires a remote web page to be loaded in the browser, making it particularly dangerous in scenarios where users visit compromised websites or are subjected to drive-by attacks.
The operational impact of CVE-2021-21215 extends beyond simple UI spoofing, as it fundamentally weakens the browser's security model and user protection mechanisms. Users who encounter malicious web pages could be tricked into believing that their browser is displaying legitimate security warnings when in fact they are being deceived by attacker-controlled content. This deception could lead to users inadvertently entering credentials into malicious forms, clicking on fraudulent security alerts, or making other unsafe decisions that compromise their security. The vulnerability affects all Chrome users running versions prior to 90.0.4430.72, making it a widespread concern across both individual users and enterprise environments. Security researchers have noted that this vulnerability aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter: PowerShell, as it involves the manipulation of browser security interfaces through script-based attacks, though the specific execution mechanism is more accurately described as HTML-based UI manipulation rather than PowerShell scripting. The potential for credential theft, phishing success, and user deception makes this vulnerability particularly dangerous in targeted attacks where attackers seek to exploit user trust in browser security warnings.
Mitigation strategies for CVE-2021-21215 center around immediate browser updates to version 90.0.4430.72 or later, which contains the necessary patches to address the improper security UI handling. Organizations should implement comprehensive patch management procedures to ensure all Chrome installations are updated promptly, particularly in enterprise environments where users may be running outdated browser versions. Additionally, security teams should monitor for any attempts to exploit this vulnerability through web-based attacks and implement web filtering solutions that can block access to known malicious domains. Network administrators should consider implementing browser security policies that restrict the ability of web pages to manipulate browser UI elements, though such restrictions may impact legitimate web functionality. Users should be educated about the importance of keeping their browsers updated and should be trained to recognize suspicious security warnings that may be spoofed by attackers. The vulnerability serves as a reminder of the critical importance of maintaining current browser security implementations and highlights the need for continuous security monitoring and patch management processes. Organizations should also consider implementing security awareness training programs that specifically address the risks associated with UI spoofing attacks and the importance of verifying security warnings through multiple verification methods rather than relying solely on browser-provided notifications.