CVE-2021-21172 in Edge
Summary
by MITRE • 03/10/2021
Insufficient policy enforcement in File System API in Google Chrome on Windows prior to 89.0.4389.72 allowed a remote attacker to bypass filesystem restrictions via a crafted HTML page.
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Analysis
by VulDB Data Team • 03/29/2021
The vulnerability identified as CVE-2021-21172 represents a critical security flaw in Google Chrome's implementation of the File System API on Windows operating systems. This issue stems from insufficient policy enforcement mechanisms that govern how web applications interact with the local file system through browser APIs. The flaw specifically affects Chrome versions prior to 89.0.4389.72, creating a persistent security risk for users who remain on outdated browser versions. The vulnerability operates at the intersection of web browser security model implementation and operating system access controls, where proper isolation between web content and local file system operations has been compromised.
The technical exploitation of this vulnerability occurs through a crafted HTML page that leverages the File System API to bypass established security boundaries. Attackers can construct malicious web pages that manipulate the browser's file system access controls, potentially allowing unauthorized read, write, or execute operations on local files. This bypass mechanism exploits the gap between the expected security policies and the actual enforcement mechanisms within Chrome's implementation. The flaw essentially allows a remote attacker to circumvent the typical sandboxing constraints that should prevent web content from accessing arbitrary files on the user's local system, effectively undermining the browser's security model.
From an operational impact perspective, this vulnerability creates significant risks for end users and organizations. Successful exploitation could enable attackers to access sensitive local files, modify system configurations, or even execute arbitrary code within the context of the user's browser session. The attack vector is particularly dangerous because it requires only a web page visit, making it highly effective for phishing campaigns or drive-by attacks. Organizations with users running vulnerable Chrome versions face potential data breaches, system compromise, and lateral movement opportunities for threat actors. The vulnerability's impact extends beyond individual users to enterprise environments where browser security is a critical component of overall security posture.
Mitigation strategies for CVE-2021-21172 primarily focus on immediate browser updates to versions 89.0.4389.72 or later where the security flaw has been addressed. System administrators should implement comprehensive patch management policies to ensure all Chrome installations are updated promptly. Additional protective measures include browser hardening configurations, implementation of content security policies, and network-level controls such as web proxies that can filter malicious content. Organizations should also consider implementing user education programs to raise awareness about visiting untrusted websites. This vulnerability aligns with CWE-284 Access Control Issues, specifically addressing insufficient enforcement of access control policies, and maps to ATT&CK technique T1059 Command and Scripting Interpreter for potential exploitation scenarios involving local file system access. The remediation process should include verification of patch deployment and monitoring for any indicators of compromise related to file system access anomalies.