CVE-2018-6152 in Chrome
Summary
by MITRE
The implementation of the Page.downloadBehavior backend unconditionally marked downloaded files as safe, regardless of file type in Google Chrome prior to 66.0.3359.106 allowed an attacker who convinced a user to install a malicious extension to potentially perform a sandbox escape via a crafted HTML page and user interaction.
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Analysis
by VulDB Data Team • 06/13/2023
The vulnerability identified as CVE-2018-6152 represents a critical sandbox escape flaw within Google Chrome's implementation of the Page.downloadBehavior backend functionality. This issue existed in Chrome versions prior to 66.0.3359.106 and fundamentally compromised the browser's security model by allowing malicious extensions to bypass sandbox restrictions. The vulnerability stems from the improper handling of file download behaviors where the system unconditionally marked all downloaded files as safe regardless of their actual content or type, creating a dangerous trust relationship between the browser and potentially malicious files.
The technical flaw manifests in how Chrome's download system processes file safety verification during the downloadBehavior implementation. When a user interacts with a crafted HTML page that triggers a download through the Page.downloadBehavior API, the browser fails to perform proper file type analysis or content inspection before marking the file as safe. This unconditional marking bypasses Chrome's normal security checks that would typically analyze file signatures, execute virus scans, or apply content-based safety assessments. The vulnerability specifically affects the browser's sandboxing mechanism by allowing malicious extensions to create or modify files in ways that would normally be restricted, effectively breaking the isolation between the browser's sandboxed environment and the underlying operating system.
From an operational impact perspective, this vulnerability enables attackers to execute sophisticated sandbox escape techniques through social engineering campaigns that convince users to install malicious browser extensions. The attack requires user interaction with a crafted HTML page that triggers the vulnerable download behavior, but once successful, it allows the malicious extension to perform actions that should be restricted within the browser's security boundaries. This could potentially lead to full system compromise, as the attacker gains access to file system operations, network communications, and other privileged functions that are normally protected by Chrome's sandbox architecture. The vulnerability creates a persistent threat vector that can be exploited across multiple user sessions and persists until the user updates their browser to a patched version.
The security implications of CVE-2018-6152 align with CWE-20, which describes improper input validation in software systems, and relates to ATT&CK technique T1059 for executing malicious code through browser-based attacks. Organizations and users affected by this vulnerability should immediately update to Chrome version 66.0.3359.106 or later, which implements proper file safety verification in the downloadBehavior implementation. Additional mitigations include implementing strict browser extension policies, disabling unnecessary browser extensions, and conducting regular security audits of installed extensions. The vulnerability also highlights the importance of proper sandbox boundary enforcement and the need for comprehensive file validation mechanisms in browser security architectures. Security teams should monitor for exploitation attempts through web-based attack vectors and ensure that browser security updates are deployed promptly across all organizational endpoints to prevent potential compromise.