CVE-2017-7831 in Firefox
Summary
by MITRE
A vulnerability where the security wrapper does not deny access to some exposed properties using the deprecated "_exposedProps_" mechanism on proxy objects. These properties should be explicitly unavailable to proxy objects. This vulnerability affects Firefox < 57.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 03/22/2023
The vulnerability described in CVE-2017-7831 represents a critical access control flaw within the Firefox browser's security architecture, specifically affecting versions prior to 57. This issue stems from the improper handling of proxy object security mechanisms, where the security wrapper fails to properly restrict access to exposed properties through a deprecated mechanism known as "exposedProps". The vulnerability exists at the intersection of JavaScript proxy object handling and browser security model implementation, creating a potential pathway for privilege escalation attacks.
The technical flaw manifests in Firefox's handling of JavaScript proxy objects where the deprecated "exposedProps" mechanism should have been completely disabled or restricted to prevent unauthorized access to internal browser properties. However, the security wrapper implementation contained a logic error that allowed certain exposed properties to remain accessible to proxy objects when they should have been explicitly denied. This creates a situation where malicious JavaScript code could potentially access sensitive browser internals through proxy objects that should have been isolated from such access. The vulnerability directly relates to CWE-284, which addresses improper access control in software systems, and specifically targets the security boundaries that should exist between different privilege levels within the browser's JavaScript execution environment.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could enable attackers to bypass security restrictions that are fundamental to browser sandboxing. When proxy objects can access properties that should remain hidden from external access, it undermines the core security model of Firefox's JavaScript engine. An attacker could potentially leverage this flaw to access internal browser APIs, manipulate privileged objects, or gain unauthorized access to sensitive data that should be protected from user-space JavaScript execution. This vulnerability particularly affects the browser's ability to maintain proper isolation between different security contexts, potentially allowing malicious code to escalate privileges or access restricted functionality that should only be available to the browser's core components.
Mitigation strategies for CVE-2017-7831 focus primarily on updating to Firefox version 57 or later, where the security wrapper implementation has been corrected to properly deny access to the deprecated "exposedProps" mechanism on proxy objects. Organizations should also implement additional security measures such as content security policies, regular browser updates, and monitoring for suspicious JavaScript behavior that might attempt to exploit similar proxy-related vulnerabilities. From an ATT&CK perspective, this vulnerability could be categorized under technique T1059.007 for JavaScript execution and T1068 for privilege escalation, as it enables attackers to bypass security controls that should prevent unauthorized access to privileged browser functionality. Security teams should also consider implementing browser hardening measures and monitoring for unusual proxy object usage patterns that might indicate exploitation attempts.