CVE-2021-21147 in Chrome
Summary
by MITRE • 02/09/2021
Inappropriate implementation in Skia in Google Chrome prior to 88.0.4324.146 allowed a local attacker to spoof the contents of the Omnibox (URL bar) via a crafted HTML page.
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Analysis
by VulDB Data Team • 02/26/2021
The vulnerability CVE-2021-21147 represents a critical security flaw in the Skia graphics rendering engine component of Google Chrome browsers. This issue stems from an inappropriate implementation that enables local attackers to manipulate the visual representation of the Omnibox, which is the primary address bar where users enter URLs and view website information. The flaw exists in Chrome versions prior to 88.0.4324.146, making a significant portion of the browser user base susceptible to this deception attack. The vulnerability specifically targets the rendering and display mechanisms that control how the address bar content is presented to users, creating a potential avenue for phishing and social engineering attacks where malicious actors could trick users into believing they are visiting legitimate websites when they are actually navigating to compromised locations.
The technical exploitation of this vulnerability occurs through the manipulation of HTML content that leverages flaws in how Skia handles rendering operations for the browser interface elements. When a user visits a specially crafted webpage, the malicious HTML code can influence the visual presentation of the Omnibox, potentially displaying fake domain names, URLs, or other identifying information that does not correspond to the actual website being accessed. This spoofing capability operates at the graphical rendering level rather than the network protocol level, making it particularly insidious as it can bypass traditional security mechanisms that focus on network-level validation. The vulnerability demonstrates weaknesses in input validation and output sanitization within the Skia graphics library, which is responsible for rendering various user interface components in Chrome. According to CWE classification, this represents a variant of CWE-20: Improper Input Validation, specifically manifesting in the context of user interface rendering where the system fails to properly validate or sanitize visual elements that users interact with directly.
The operational impact of CVE-2021-21147 extends beyond simple visual deception to potentially enable sophisticated phishing attacks and credential theft operations. Users who are tricked by the spoofed Omnibox content may unknowingly enter sensitive information on what they perceive to be legitimate websites, creating opportunities for data breaches and identity theft. The local attack vector means that the malicious code only needs to be present on the victim's device to exploit the vulnerability, making it particularly dangerous in environments where users may inadvertently visit compromised websites or where malware has already established presence on the system. This vulnerability directly impacts the browser's security model by undermining user confidence in the authenticity of website information displayed in the address bar, which is a fundamental security feature designed to protect users from malicious websites. The attack scenario typically involves a user visiting a malicious website that contains carefully crafted HTML elements designed to manipulate the Skia rendering engine's behavior, causing the browser to display misleading information in the Omnibox.
Mitigation strategies for CVE-2021-21147 primarily focus on immediate browser updates to versions 88.0.4324.146 and later, which contain patches addressing the underlying Skia implementation flaws. System administrators should prioritize the deployment of these security updates across all affected Chrome installations, particularly in enterprise environments where multiple users may be exposed to the vulnerability. Additional protective measures include implementing browser security extensions that monitor for suspicious rendering behaviors and establishing user education programs to help individuals recognize potential phishing attempts. Organizations should also consider implementing network-level monitoring to detect unusual traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date security patches and demonstrates how flaws in graphics rendering libraries can create unexpected security vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to techniques involving social engineering through user interface manipulation and privilege escalation through browser-based attacks, emphasizing the need for comprehensive security approaches that address both network-level and application-level threats. The fix implemented by Google likely involved strengthening input validation mechanisms within the Skia library and improving the isolation between different rendering contexts to prevent one component from manipulating the visual presentation of critical user interface elements.