CVE-2016-7479 in PHP
Summary
by MITRE
In all versions of PHP 7, during the unserialization process, resizing the 'properties' hash table of a serialized object may lead to use-after-free. A remote attacker may exploit this bug to gain arbitrary code execution.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2016-7479 represents a critical use-after-free condition that emerged in all versions of PHP 7 during the object unserialization process. This flaw resides within the internal handling of serialized data structures and specifically affects the management of property hash tables within serialized objects. The vulnerability stems from improper memory management practices that occur when PHP attempts to resize hash tables during deserialization operations, creating opportunities for attackers to manipulate memory layout and execute arbitrary code.
This security issue operates at the intersection of memory corruption and object serialization vulnerabilities, with the technical flaw manifesting as a race condition in the hash table resizing mechanism. During the unserialization process, PHP allocates memory for object properties and maintains them in hash tables for efficient access. When the system needs to expand or contract these hash tables, it may free previously allocated memory regions while still maintaining references to them. This creates a window where attacker-controlled data can be used to manipulate the freed memory, leading to potential code execution.
The operational impact of this vulnerability is severe and affects any application running PHP 7 that processes untrusted serialized data from external sources. Attackers can exploit this by crafting malicious serialized objects that, when processed by the vulnerable PHP version, trigger the hash table resizing operation and subsequently cause the use-after-free condition. This allows for arbitrary code execution with the privileges of the web server process, potentially leading to complete system compromise. The vulnerability is particularly dangerous in web applications that accept serialized input from users or external services, making it a prime target for remote code execution attacks.
The flaw aligns with CWE-416, which describes use-after-free vulnerabilities, and demonstrates characteristics consistent with the ATT&CK technique T1548.001 for privilege escalation and T1059 for command and scripting interpreter. Organizations using PHP 7 should immediately upgrade to patched versions to mitigate this risk, as the vulnerability affects all PHP 7.x releases and can be exploited remotely without authentication. Additionally, implementing proper input validation and sanitization of serialized data, along with restricting the use of unserialize() functions where possible, provides additional defense-in-depth measures. The vulnerability highlights the critical importance of proper memory management in interpreted languages and the need for thorough testing of serialization mechanisms in web applications.