CVE-2014-8142 in PHP
Summary
by MITRE
Use-after-free vulnerability in the process_nested_data function in ext/standard/var_unserializer.re in PHP before 5.4.36, 5.5.x before 5.5.20, and 5.6.x before 5.6.4 allows remote attackers to execute arbitrary code via a crafted unserialize call that leverages improper handling of duplicate keys within the serialized properties of an object, a different vulnerability than CVE-2004-1019.
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Analysis
by VulDB Data Team • 03/02/2022
The CVE-2014-8142 vulnerability represents a critical use-after-free flaw in PHP's serialization handling mechanism that has significant implications for web application security. This vulnerability exists within the process_nested_data function located in the ext/standard/var_unserializer.re file of PHP's source code, affecting multiple versions including PHP 5.4.x before 5.4.36, 5.5.x before 5.5.20, and 5.6.x before 5.6.4. The flaw specifically manifests when PHP processes serialized data containing duplicate keys within object properties, creating a scenario where memory that has been freed is subsequently accessed, leading to potential code execution.
The technical nature of this vulnerability stems from improper memory management during the unserialization process when duplicate keys are encountered in serialized objects. When PHP encounters duplicate keys during the deserialization of object properties, the internal handling mechanism fails to properly manage memory allocation and deallocation, resulting in a use-after-free condition. This occurs because the system allocates memory for object properties, processes duplicate keys incorrectly, and then frees the memory while still maintaining references to that freed memory location. Attackers can exploit this by crafting malicious serialized data containing carefully constructed duplicate keys that manipulate the memory layout to achieve arbitrary code execution.
The operational impact of CVE-2014-8142 is severe and far-reaching, as it allows remote attackers to execute arbitrary code on vulnerable systems without requiring authentication. This vulnerability can be exploited through any application that accepts user input and processes it through PHP's unserialize function, making it particularly dangerous in web applications that handle user-provided data. The attack vector typically involves sending a crafted serialized object through HTTP parameters, cookies, or file uploads, where the unserialize function processes the malicious data and triggers the use-after-free condition. This vulnerability aligns with CWE-416, which specifically addresses the use of freed memory, and represents a classic example of how improper memory management can lead to remote code execution.
The exploitation of this vulnerability follows patterns consistent with the ATT&CK framework's privilege escalation and code execution techniques, particularly targeting the execution phase where attackers can leverage memory corruption vulnerabilities. The vulnerability differs from CVE-2004-1019 in its specific implementation details, as it focuses on the handling of duplicate keys rather than the broader serialization mechanism. Organizations running affected PHP versions face significant risk, as this vulnerability can be exploited in various contexts including web applications, API endpoints, and any system that relies on PHP's serialization functionality for data exchange. The remote nature of the exploit means that attackers do not need physical access to the system, making it particularly dangerous for publicly accessible web applications.
Mitigation strategies for CVE-2014-8142 primarily involve upgrading to patched versions of PHP, specifically PHP 5.4.36, 5.5.20, or 5.6.4, respectively. System administrators should also implement additional security measures including disabling unserialize functions when possible, validating and sanitizing all user input before processing, and implementing proper input validation to prevent malicious serialized data from reaching the unserialize function. The vulnerability demonstrates the importance of secure coding practices and proper memory management in interpreted languages, highlighting how seemingly minor implementation flaws can result in critical security vulnerabilities. Organizations should also consider implementing network segmentation and monitoring for unusual serialization activity that might indicate exploitation attempts.