CVE-2015-6832 in PHP
Summary
by MITRE
Use-after-free vulnerability in the SPL unserialize implementation in ext/spl/spl_array.c in PHP before 5.4.44, 5.5.x before 5.5.28, and 5.6.x before 5.6.12 allows remote attackers to execute arbitrary code via crafted serialized data that triggers misuse of an array field.
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Analysis
by VulDB Data Team • 07/03/2022
The CVE-2015-6832 vulnerability represents a critical use-after-free flaw within PHP's Standard PHP Library implementation, specifically affecting the unserialize function in the spl_array.c file. This vulnerability exists in PHP versions prior to 5.4.44, 5.5.28, and 5.6.12, making it a widespread issue across multiple PHP release lines. The flaw manifests when PHP processes crafted serialized data that exploits improper memory management during the unserialization of array objects. The vulnerability is classified under CWE-416 as a Use-After-Free condition, which occurs when a program continues to reference memory after it has been freed, creating opportunities for memory corruption and arbitrary code execution.
The technical exploitation of this vulnerability relies on the improper handling of array fields during the unserialize process within the SPL extension. When PHP encounters maliciously crafted serialized data, the SPL array implementation fails to properly validate or manage the memory references associated with array objects, leading to a situation where freed memory can be accessed and manipulated by an attacker. This memory corruption can be leveraged to overwrite critical memory locations, manipulate program flow, or execute arbitrary code with the privileges of the PHP process. The vulnerability specifically targets the unserialize function's behavior when processing array data structures, making it particularly dangerous in applications that deserialize user-supplied input without proper validation.
The operational impact of CVE-2015-6832 is severe and far-reaching, as it enables remote code execution attacks that can compromise entire web applications and servers. Attackers can craft serialized data payloads that, when processed by vulnerable PHP applications, trigger the use-after-free condition and potentially gain full system control. This vulnerability is particularly dangerous in web environments where user input is commonly deserialized without proper sanitization, making it a prime target for exploitation in web application attacks. The vulnerability affects not only standalone PHP applications but also content management systems, web frameworks, and any application that relies on PHP's serialization functionality for data persistence or communication. Organizations running vulnerable PHP versions are at significant risk of data breaches, system compromise, and unauthorized access to sensitive information.
Mitigation strategies for CVE-2015-6832 focus primarily on immediate patching and application hardening measures. The most effective solution involves upgrading to patched PHP versions, specifically PHP 5.4.44, 5.5.28, or 5.6.12, which contain the necessary fixes for the use-after-free condition. Organizations should also implement strict input validation and sanitization practices, particularly for serialized data that originates from untrusted sources. The principle of least privilege should be enforced by running PHP processes with minimal required permissions and by implementing proper memory management practices in application code. Additionally, security monitoring should be enhanced to detect unusual deserialization patterns and potential exploitation attempts. Organizations should also consider implementing web application firewalls and intrusion detection systems that can identify and block malicious serialized data payloads, following ATT&CK framework techniques for defense against code injection and privilege escalation attacks.