CVE-2016-5773 in macOS
Summary
by MITRE
php_zip.c in the zip extension in PHP before 5.5.37, 5.6.x before 5.6.23, and 7.x before 7.0.8 improperly interacts with the unserialize implementation and garbage collection, which allows remote attackers to execute arbitrary code or cause a denial of service (use-after-free and application crash) via crafted serialized data containing a ZipArchive object.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5773 represents a critical security flaw within PHP's zip extension that affects multiple versions of the PHP runtime environment. This issue stems from improper handling of serialized data within the zip extension's interaction with PHP's unserialize mechanism and garbage collection processes. The vulnerability exists in PHP versions prior to 5.5.37, 5.6.23, and 7.0.8, creating a widespread attack surface across numerous web applications that rely on PHP for their operation. The flaw specifically manifests when PHP processes crafted serialized data containing ZipArchive objects, leading to potentially catastrophic consequences for affected systems.
The technical root cause of this vulnerability lies in the improper management of memory references during the deserialization process of ZipArchive objects within PHP's zip extension. When PHP encounters serialized data containing a ZipArchive object, the interaction between the unserialize implementation and PHP's garbage collection system creates conditions where memory locations may be freed while still being referenced. This memory management inconsistency results in a use-after-free condition that can be exploited by remote attackers to execute arbitrary code on the target system. The vulnerability is particularly dangerous because it leverages the legitimate unserialize functionality that many PHP applications use for data persistence and object reconstruction, making it difficult to detect and prevent through traditional security measures.
The operational impact of CVE-2016-5773 extends beyond simple remote code execution to include potential denial of service conditions that can crash applications and render them unavailable to legitimate users. Attackers can craft malicious serialized data that, when processed by vulnerable PHP applications, triggers the use-after-free condition and allows for arbitrary code execution with the privileges of the web server process. This capability enables attackers to gain unauthorized access to sensitive data, modify application behavior, or completely compromise the affected system. The vulnerability affects any PHP application that processes user-provided serialized data, particularly those that deserialize data from forms, cookies, or API responses without proper validation and sanitization. The attack vector is particularly concerning because it can be exploited through common web application interfaces without requiring special privileges or access to the underlying system.
Organizations affected by this vulnerability should prioritize immediate patching of their PHP installations to versions that contain the necessary security fixes. The remediation process involves upgrading to PHP 5.5.37, 5.6.23, or 7.0.8, depending on the current version in use. Additionally, administrators should implement defensive measures such as input validation and sanitization for all serialized data, particularly data that originates from untrusted sources. The vulnerability aligns with CWE-416, which describes use-after-free conditions, and represents a significant concern within the ATT&CK framework under the execution and privilege escalation tactics. Security teams should also consider implementing application firewalls and monitoring systems to detect unusual deserialization patterns that may indicate exploitation attempts. Regular security assessments and code reviews should focus on identifying any custom serialization logic that might be vulnerable to similar memory management issues.