CVE-2016-4473 in PHP
Summary
by MITRE
/ext/phar/phar_object.c in PHP 7.0.7 and 5.6.x allows remote attackers to execute arbitrary code. NOTE: Introduced as part of an incomplete fix to CVE-2015-6833.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2016-4473 represents a critical remote code execution flaw within PHP's phar extension that emerged as an incomplete remediation to a previous vulnerability. This issue affects PHP versions 7.0.7 and 5.6.x, creating a dangerous attack surface that allows remote adversaries to execute arbitrary code on vulnerable systems. The flaw resides within the phar_object.c file, which handles phar archive processing functionality, making it particularly dangerous as phar archives are commonly used for packaging and distribution in PHP applications.
The technical nature of this vulnerability stems from inadequate input validation and improper handling of phar archive metadata during deserialization processes. When PHP processes a maliciously crafted phar archive, the flawed implementation in phar_object.c fails to properly sanitize user-supplied data, allowing attackers to inject malicious payloads that execute with the privileges of the web server process. This vulnerability specifically exploits the way PHP handles phar archive objects during object deserialization, bypassing security mechanisms that were intended to prevent such attacks. The incomplete fix for CVE-2015-6833 created a regression that reintroduced similar attack vectors, making this vulnerability particularly concerning for systems that rely on phar archive functionality.
The operational impact of CVE-2016-4473 is severe and far-reaching, as it provides attackers with complete control over affected systems without requiring authentication. Remote code execution capabilities enable attackers to perform various malicious activities including data exfiltration, privilege escalation, system compromise, and deployment of additional malware. The vulnerability is particularly dangerous in web environments where phar archives are commonly processed, as it can be exploited through simple HTTP requests that upload or process malicious phar files. This attack vector can be leveraged in automated exploitation campaigns, making it a high-priority target for threat actors seeking to compromise web applications that handle user-uploaded content or external archive processing.
Organizations should implement immediate mitigations including upgrading to PHP versions that contain proper fixes for this vulnerability, which are available in PHP 7.0.8 and 5.6.23. Additionally, administrators should disable phar extension functionality when not required, implement strict input validation for all phar archive processing, and monitor system logs for suspicious phar-related activities. The vulnerability aligns with CWE-119 and CWE-121 categories related to memory corruption and buffer overflow conditions, and maps to ATT&CK techniques involving execution through compromised web applications and privilege escalation. Security teams should also consider implementing web application firewalls to detect and block malicious phar archive requests, as well as conducting comprehensive vulnerability assessments to identify systems that may be processing untrusted phar archives.