CVE-2020-6399 in Chrome
Summary
by MITRE
Insufficient policy enforcement in AppCache in Google Chrome prior to 80.0.3987.87 allowed a remote attacker to leak cross-origin data via a crafted HTML page.
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability identified as CVE-2020-6399 represents a critical security flaw in Google Chrome's AppCache implementation that existed prior to version 80.0.3987.87. This issue stems from inadequate policy enforcement mechanisms within the browser's application cache system, which is designed to store web applications and their resources for offline access. The AppCache functionality, while intended to improve user experience by enabling offline web application usage, created an unintended attack vector that compromised cross-origin data integrity. The flaw specifically affects how Chrome handles cache management across different origins, creating a pathway for malicious actors to exploit the system's permission model.
The technical exploitation of this vulnerability occurs through a crafted HTML page that leverages the insufficient policy enforcement to access and leak data from different origins. When a user visits a malicious website, the attacker's page can manipulate the AppCache system to retrieve cached resources from other domains that should normally be restricted due to cross-origin policies. This breach of isolation allows for unauthorized data exfiltration, potentially including sensitive information from authenticated sessions or private user data. The vulnerability operates at the browser's core caching mechanism level, making it particularly dangerous as it bypasses traditional web security boundaries that should prevent such cross-origin access.
From an operational impact perspective, this vulnerability poses significant risks to user privacy and data security across the Chrome ecosystem. Attackers could potentially harvest cookies, session tokens, or other sensitive data from cached resources of visited websites, particularly affecting users who access multiple applications or services through a single browser instance. The exploitation could lead to session hijacking, credential theft, or unauthorized access to protected resources. Given Chrome's widespread adoption across desktop and mobile platforms, the potential attack surface for this vulnerability is extensive, affecting millions of users who rely on the browser for daily web activities. The issue particularly impacts enterprise environments where users may access sensitive corporate applications through Chrome, creating potential pathways for data leakage.
The vulnerability aligns with CWE-284, which addresses inadequate access control mechanisms, and relates to ATT&CK technique T1071.004 for application layer protocol usage. Organizations should implement immediate mitigation strategies including updating Chrome to version 80.0.3987.87 or later, where Google has addressed the policy enforcement gaps in AppCache implementation. Network administrators should monitor for suspicious web traffic patterns that might indicate exploitation attempts, while security teams should consider implementing additional browser hardening measures. The fix implemented by Google involved strengthening the policy enforcement mechanisms within the AppCache system to properly enforce cross-origin restrictions and prevent unauthorized access to cached resources from different domains. This remediation ensures that cached application data remains properly isolated according to standard web security principles and browser sandboxing requirements.