CVE-2013-0798 in Firefox
Summary
by MITRE
Mozilla Firefox before 20.0 on Android uses world-writable and world-readable permissions for the app_tmp installation directory in the local filesystem, which allows attackers to modify add-ons before installation via an application that leverages the time window during which app_tmp is used.
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Analysis
by VulDB Data Team • 01/31/2018
The vulnerability identified as CVE-2013-0798 represents a critical security flaw in Mozilla Firefox versions prior to 20.0 on Android platforms. This issue stems from improper file system permissions assigned to the app_tmp installation directory, creating a persistent security weakness that attackers can exploit to manipulate add-on installations. The vulnerability specifically affects the Android implementation of Firefox, where the temporary directory used during installation processes is configured with overly permissive access controls that grant world-writable and world-readable permissions. This misconfiguration creates a window of opportunity for malicious actors to intercept and modify add-on components before they are properly installed, fundamentally compromising the integrity of the browser's extension ecosystem.
The technical exploitation of this vulnerability occurs through a time-based attack vector that leverages the temporal gap between when the app_tmp directory is created and when the add-on installation process completes. During this window, attackers can place malicious files in the world-writable directory, which will then be executed or installed as legitimate components. This process directly violates fundamental security principles of least privilege and proper access control enforcement. The flaw aligns with CWE-732, which addresses inadequate permissions for critical resources, and represents a classic example of insecure temporary file handling that enables privilege escalation attacks. The vulnerability essentially allows an attacker to inject malicious code into the browser's extension system, potentially leading to complete system compromise through the execution of unauthorized add-ons.
The operational impact of CVE-2013-0798 extends beyond simple data corruption or unauthorized access, as it fundamentally undermines the trust model of Firefox's add-on architecture. When attackers can modify add-ons before installation, they gain the ability to execute arbitrary code with the privileges of the browser application, potentially leading to full system compromise. This vulnerability enables sophisticated attack scenarios including the installation of persistent backdoors, keyloggers, or other malicious extensions that can operate undetected within the browser environment. The attack surface is particularly concerning given that add-ons often require elevated permissions to function properly, making them attractive targets for exploitation. This weakness directly maps to ATT&CK technique T1106, which covers the use of legitimate credentials and system tools for execution, as the attacker leverages the legitimate installation process to achieve malicious objectives.
Mitigation strategies for this vulnerability require immediate remediation through the upgrade of Firefox to version 20.0 or later, where proper file system permissions have been implemented. Organizations should also implement additional monitoring of the app_tmp directory for unauthorized modifications and consider implementing file integrity checking mechanisms to detect tampering. System administrators should review and enforce proper file permissions on all temporary directories within the Android environment, ensuring that temporary files are not accessible for modification by unauthorized users. The fix implemented by Mozilla involved correcting the permission settings for the app_tmp directory to ensure that only the intended application processes can write to it, thereby closing the time window exploitation opportunity. Regular security audits of mobile browser environments should include verification of temporary file permissions and comprehensive testing of installation processes to prevent similar vulnerabilities from emerging in future releases.