CVE-2016-4072 in Mac OS X
Summary
by MITRE
The Phar extension in PHP before 5.5.34, 5.6.x before 5.6.20, and 7.x before 7.0.5 allows remote attackers to execute arbitrary code via a crafted filename, as demonstrated by mishandling of \0 characters by the phar_analyze_path function in ext/phar/phar.c.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2016-4072 represents a critical remote code execution flaw within PHP's Phar extension, affecting multiple PHP version streams including 5.5.x, 5.6.x, and 7.x prior to specific patch releases. This vulnerability stems from improper handling of special characters within filenames during the phar_analyze_path function execution in the ext/phar/phar.c source file. The flaw allows attackers to craft malicious filenames containing null characters that bypass normal validation checks, ultimately enabling arbitrary code execution on vulnerable systems. The technical nature of this vulnerability places it squarely within the realm of input validation failures and improper handling of binary data, which aligns with CWE-170, specifically the improper handling of null characters in strings. This weakness creates a pathway for attackers to manipulate the Phar extension's internal processing logic, potentially leading to complete system compromise when the extension is enabled and used in web applications.
The operational impact of CVE-2016-4072 extends far beyond simple code execution, as it provides attackers with a mechanism to gain persistent access to affected systems. When exploited, this vulnerability allows remote attackers to execute arbitrary commands with the privileges of the web server process, potentially enabling further reconnaissance, lateral movement, and data exfiltration. The vulnerability is particularly dangerous because it can be triggered through standard file upload mechanisms or by manipulating Phar archive creation processes, making it applicable to a wide range of web applications that utilize PHP's Phar extension. The attack vector requires minimal privileges and can be automated, making it attractive to threat actors seeking to compromise web infrastructure. According to ATT&CK framework, this vulnerability maps to T1059.007 for remote code execution and T1566 for initial access through web applications, demonstrating how this flaw can serve as a foundational entry point for broader attacks.
Mitigation strategies for CVE-2016-4072 primarily focus on immediate patching of affected PHP installations to versions that contain the necessary security fixes. Organizations should prioritize updating their PHP environments to versions 5.5.34, 5.6.20, or 7.0.5 respectively, depending on their current PHP version. Additionally, administrators should consider disabling the Phar extension entirely if it is not required for application functionality, as this provides a strong defense-in-depth approach. Network-level protections such as web application firewalls can help detect and block malicious filename patterns, though these should not be relied upon as the sole mitigation. Input validation and sanitization practices should be enhanced to specifically check for null characters and other problematic sequences in filenames. Security monitoring should include detection of unusual Phar extension usage patterns and file creation activities that might indicate exploitation attempts. The vulnerability also underscores the importance of maintaining current security patches and implementing robust application security testing procedures to identify similar weaknesses in custom code that might interact with PHP's extension system.