CVE-2016-5771 in macOS
Summary
by MITRE
spl_array.c in the SPL extension in PHP before 5.5.37 and 5.6.x before 5.6.23 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.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-5771 resides within the SPL (Standard PHP Library) extension of PHP, specifically in the spl_array.c file that governs array handling functionalities. This flaw represents a critical security issue affecting PHP versions prior to 5.5.37 and 5.6.x versions before 5.6.23, where the interaction between the unserialize implementation and PHP's garbage collection mechanism creates exploitable conditions. The vulnerability manifests through improper memory management during object deserialization processes, creating opportunities for malicious actors to manipulate the runtime behavior of PHP applications.
The technical root cause of this vulnerability stems from a use-after-free condition that occurs when PHP processes specially crafted serialized data containing SPL array objects. During the unserialization process, the garbage collection system attempts to clean up memory associated with objects that have already been accessed, leading to scenarios where freed memory locations are still referenced by subsequent operations. This memory corruption vulnerability allows attackers to execute arbitrary code by carefully constructing serialized payloads that manipulate the object lifecycle and memory layout during deserialization. The flaw specifically affects PHP's internal array handling mechanisms within the SPL extension, where the interaction between the __wakeup() magic method and garbage collection creates opportunities for memory corruption.
The operational impact of CVE-2016-5771 is severe and multifaceted, encompassing both remote code execution and denial of service capabilities. Attackers can leverage this vulnerability to gain arbitrary code execution on affected systems, potentially leading to complete system compromise and unauthorized access to sensitive data. The use-after-free condition can also result in application crashes and denial of service scenarios, making it a significant threat to system availability and stability. This vulnerability affects web applications that utilize PHP's serialization functions and SPL array objects, particularly those that deserialize user-provided input without proper validation or sanitization, creating a broad attack surface across numerous PHP-based applications and frameworks.
Organizations should implement immediate mitigations including upgrading to PHP versions 5.5.37 or 5.6.23 and later, which contain the necessary patches to address the memory management issues within the SPL extension. Additionally, applications should avoid deserializing untrusted data whenever possible, implementing strict input validation and sanitization measures before processing serialized content. The vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a classic example of memory safety issues that can be exploited through object-oriented programming constructs in scripting languages. From an ATT&CK framework perspective, this vulnerability maps to technique T1059.007 for execution through PHP and T1499.004 for denial of service, making it a significant concern for both offensive and defensive security operations.