CVE-2009-3372 in Firefox
Summary
by MITRE
Mozilla Firefox before 3.0.15 and 3.5.x before 3.5.4, and SeaMonkey before 2.0, allows remote attackers to execute arbitrary code via a crafted regular expression in a Proxy Auto-configuration (PAC) file.
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Analysis
by VulDB Data Team • 08/24/2021
The vulnerability described in CVE-2009-3372 represents a critical security flaw in Mozilla Firefox and SeaMonkey browsers that enables remote code execution through malicious proxy configuration files. This vulnerability specifically affects versions prior to Firefox 3.0.15 and 3.5.x series 3.5.4, as well as SeaMonkey versions before 2.0. The issue stems from improper handling of regular expressions within Proxy Auto-configuration files, creating a pathway for attackers to craft malicious PAC files that can trigger arbitrary code execution on vulnerable systems. The flaw operates at the intersection of web browser security and network configuration handling, making it particularly dangerous as it can be exploited through standard web browsing activities when users encounter malicious proxy configurations.
The technical implementation of this vulnerability involves a buffer overflow or memory corruption issue that occurs when the browser processes crafted regular expressions within PAC files. According to CWE standards, this vulnerability maps to CWE-129, which describes improper validation of array indices, and potentially CWE-787, representing out-of-bounds write operations. The flaw exploits the way Firefox handles regular expression compilation and execution within proxy configuration contexts, where maliciously crafted patterns can cause stack corruption or heap-based memory issues that allow attackers to inject and execute arbitrary code with the privileges of the browser process. The vulnerability demonstrates a classic example of how seemingly benign configuration file processing can become a vector for sophisticated attacks.
The operational impact of this vulnerability extends beyond simple browser compromise, as successful exploitation can lead to complete system takeover when attackers leverage the browser's execution context. The attack surface is particularly wide since PAC files are often automatically downloaded and executed by browsers during network configuration processes, making user interaction unnecessary for exploitation. This vulnerability aligns with ATT&CK technique T1190, which covers exploitation of remote services through proxy configuration manipulation, and T1059, covering command and scripting interpreters. The potential for privilege escalation and lateral movement within networks makes this vulnerability particularly attractive to threat actors, as compromised browsers can serve as entry points for broader network infiltration.
Organizations and users must implement immediate mitigations to address this vulnerability, including upgrading to patched versions of Firefox and SeaMonkey browsers, as well as implementing network-level controls to prevent automatic PAC file downloads from untrusted sources. Network administrators should consider disabling automatic proxy configuration or implementing strict validation of PAC file content before execution. The recommended approach includes applying security patches promptly, monitoring network traffic for suspicious PAC file downloads, and implementing browser security policies that restrict proxy configuration capabilities. Additionally, organizations should conduct security awareness training to prevent users from inadvertently downloading malicious PAC files from compromised websites, as this vulnerability can be exploited through social engineering techniques that trick users into accepting malicious proxy configurations.