CVE-2015-0820 in Firefox
Summary
by MITRE
Mozilla Firefox before 36.0 does not properly restrict transitions of JavaScript objects from a non-extensible state to an extensible state, which allows remote attackers to bypass a Caja Compiler sandbox protection mechanism or a Secure EcmaScript sandbox protection mechanism via a crafted web site.
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Analysis
by VulDB Data Team • 03/10/2022
The vulnerability described in CVE-2015-0820 represents a critical flaw in Mozilla Firefox's JavaScript engine that undermines sandbox security mechanisms designed to protect users from malicious web content. This issue specifically affects Firefox versions prior to 36.0 and stems from improper handling of JavaScript object state transitions within the engine's object model implementation. The flaw allows attackers to manipulate the extensibility properties of JavaScript objects in ways that were not properly constrained by the browser's security architecture.
The technical root cause of this vulnerability lies in Firefox's failure to adequately enforce object extensibility restrictions during state transitions. When JavaScript objects transition from non-extensible to extensible states, the browser should maintain strict controls to prevent unauthorized modifications to object properties and methods. However, the implementation contained a gap that allowed remote attackers to exploit this behavior to escape sandboxed environments. This vulnerability specifically impacts two major sandbox protection mechanisms: the Caja Compiler sandbox and the Secure EcmaScript sandbox, both of which rely on proper object state management to maintain their security boundaries.
The operational impact of this vulnerability is severe as it provides remote attackers with a pathway to bypass critical security controls that protect users from malicious websites. Attackers can craft specifically designed web pages that leverage this object state transition flaw to gain unauthorized access to restricted JavaScript functionality. This capability enables potential exploitation of other security mechanisms, as the sandbox escape allows attackers to access privileged APIs and execute code that should normally be restricted. The vulnerability essentially creates a backdoor through which malicious actors can circumvent the browser's security model, potentially leading to full system compromise.
This vulnerability maps to CWE-245 in the Common Weakness Enumeration catalog, which specifically addresses "Unstable Object State" and improper object state management in security-critical contexts. The flaw demonstrates a classic security architecture weakness where object state transitions are not properly validated, creating opportunities for privilege escalation and sandbox bypass. From an ATT&CK framework perspective, this vulnerability corresponds to techniques involving sandbox evasion and privilege escalation through application-level flaws, specifically targeting the browser's JavaScript engine security controls. The exploitability of this vulnerability aligns with ATT&CK technique T1059.007 for JavaScript-based attacks and T1070.004 for bypassing security controls through application-specific flaws.
The recommended mitigation strategy involves upgrading to Firefox version 36.0 or later, where the object state transition handling has been properly corrected. Organizations should also implement network-level protections such as content filtering and web application firewalls to limit exposure while upgrades are pending. Browser hardening measures including disabling unnecessary JavaScript features and implementing strict content security policies can provide additional defense-in-depth. Security monitoring should focus on detecting unusual JavaScript object manipulation patterns and potential sandbox escape attempts. Regular security assessments of browser configurations and ongoing patch management processes are essential to maintain protection against similar vulnerabilities in the JavaScript engine and related security mechanisms.