CVE-2015-0231 in PHP
Summary
by MITRE
Use-after-free vulnerability in the process_nested_data function in ext/standard/var_unserializer.re in PHP before 5.4.37, 5.5.x before 5.5.21, and 5.6.x before 5.6.5 allows remote attackers to execute arbitrary code via a crafted unserialize call that leverages improper handling of duplicate numerical keys within the serialized properties of an object. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-8142.
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Analysis
by VulDB Data Team • 03/07/2022
The CVE-2015-0231 vulnerability represents a critical use-after-free condition that affects PHP versions prior to specific patch releases, fundamentally compromising the integrity of the unserialize process. This vulnerability specifically targets the process_nested_data function within the ext/standard/var_unserializer.re component of PHP, creating a dangerous scenario where memory previously freed by the application can be accessed and manipulated by malicious actors. The flaw manifests when processing serialized data containing duplicate numerical keys within object properties, exploiting an incomplete remediation of the previously disclosed CVE-2014-8142 vulnerability. The security implications are severe as this allows remote attackers to execute arbitrary code on vulnerable systems, effectively bypassing normal security boundaries and potentially leading to full system compromise. The vulnerability operates through a sophisticated manipulation of PHP's serialization mechanism where the improper handling of duplicate numerical keys creates a scenario where freed memory objects can be reused, enabling attackers to control program execution flow.
The technical exploitation of CVE-2015-0231 relies on the specific behavior of PHP's object unserialization process and how it manages memory allocation for duplicate numerical keys. When PHP encounters serialized data with duplicate numerical keys, the process_nested_data function fails to properly manage memory references, leading to a situation where objects are freed from memory but references to them remain valid. This creates a use-after-free condition that attackers can exploit by carefully crafting serialized payloads that manipulate the memory layout and force the application to execute malicious code from the freed memory regions. The vulnerability is particularly dangerous because it operates at the core of PHP's data handling mechanisms, making it difficult to detect and prevent through traditional security measures. The incomplete fix for CVE-2014-8142 left residual memory management issues that directly contribute to this vulnerability, demonstrating how remediation efforts can sometimes create new attack surfaces if not thoroughly tested and validated.
From an operational impact perspective, CVE-2015-0231 poses significant risks to web applications and servers running vulnerable PHP versions, as it enables remote code execution without requiring authentication or specific user interaction. Systems utilizing PHP for data serialization, including content management systems, web applications, and API endpoints, become immediately vulnerable to exploitation. The attack vector typically involves sending specially crafted serialized data to endpoints that process user input through PHP's unserialize function, allowing attackers to gain arbitrary code execution privileges. This vulnerability affects a broad range of PHP applications and services, from simple web forms to complex enterprise applications, making it particularly dangerous in environments where multiple applications are running on the same infrastructure. Organizations may experience complete system compromise, data breaches, and unauthorized access to sensitive information, with the potential for lateral movement within networks and persistence mechanisms.
The mitigation strategies for CVE-2015-0231 center around immediate patching of affected PHP versions to the recommended secure releases, specifically PHP 5.4.37, 5.5.21, and 5.6.5, which contain the complete fixes for this vulnerability. Organizations should also implement input validation and sanitization measures to prevent untrusted data from reaching the unserialize function, particularly when processing user-supplied input. Security monitoring should be enhanced to detect unusual patterns in serialization operations and potential exploitation attempts. Additionally, implementing proper access controls and network segmentation can help limit the potential damage from successful exploits. This vulnerability aligns with CWE-416, which describes the use of freed memory condition, and maps to ATT&CK technique T1059.007 for remote code execution through web applications. Organizations should also consider implementing application whitelisting and runtime protection mechanisms to detect and prevent exploitation attempts, as the vulnerability can be difficult to detect through traditional network-based security controls. The remediation process requires careful testing of patches to ensure that updates do not break existing application functionality while addressing the core memory management issues that enable this exploitation.