CVE-2015-8876 in PHP
Summary
by MITRE
Zend/zend_exceptions.c in PHP before 5.4.44, 5.5.x before 5.5.28, and 5.6.x before 5.6.12 does not validate certain Exception objects, which allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) or trigger unintended method execution via crafted serialized data.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2015-8876 represents a critical security flaw within the PHP runtime environment that affects multiple version branches including 5.4.x, 5.5.x, and 5.6.x series. This issue resides in the zend_exceptions.c file which forms a core component of PHP's exception handling mechanism. The vulnerability stems from inadequate validation of Exception objects during the deserialization process, creating a pathway for malicious actors to exploit the system through crafted serialized data payloads. The flaw manifests as a failure to properly validate exception objects when they are reconstructed from serialized representations, leading to potential system instability and application compromise.
The technical implementation of this vulnerability exploits the inherent weakness in PHP's object serialization and deserialization routines within its Zend Engine. When PHP processes serialized Exception objects, it fails to validate the integrity and structure of these objects before attempting to execute them. This validation gap allows attackers to craft malicious serialized data that contains malformed Exception objects with NULL pointers or invalid method references. The vulnerability specifically targets the exception handling subsystem where the application attempts to dereference NULL pointers during the execution of improperly validated exception objects, resulting in immediate application crashes or system instability. The flaw operates at the core level of PHP's execution engine, making it particularly dangerous as it can affect any application utilizing PHP's exception handling mechanisms regardless of the application's specific code implementation.
The operational impact of CVE-2015-8876 extends beyond simple denial of service conditions to potentially enable more sophisticated attack vectors. Remote attackers can leverage this vulnerability to cause complete application crashes, leading to service disruption and potential data loss. The vulnerability also presents opportunities for unintended method execution, where crafted serialized data might trigger arbitrary code execution within the application context. This capability transforms a simple denial of service into a more serious security concern that could allow attackers to gain unauthorized access to system resources or escalate privileges. The vulnerability affects web applications that utilize PHP's built-in serialization functions, particularly those that deserialize user-provided data without proper validation, making it a widespread concern across the PHP ecosystem. Organizations running affected PHP versions face significant risk of system compromise, with potential for extended downtime and data integrity issues.
The remediation approach for CVE-2015-8876 requires immediate patching of affected PHP installations to the patched versions 5.4.44, 5.5.28, and 5.6.12 respectively. Organizations should also implement comprehensive input validation measures to prevent deserialization of untrusted data, following the principle of least privilege and input sanitization practices. Security teams should monitor application logs for signs of exploitation attempts and implement proper error handling mechanisms that do not expose internal system information. The vulnerability aligns with CWE-470, which addresses the use of insecure deserialization methods, and relates to ATT&CK technique T1203, involving the exploitation of software vulnerabilities for denial of service. Organizations should also consider implementing application whitelisting and runtime protection measures to prevent unauthorized code execution, while maintaining regular security assessments to identify similar vulnerabilities within their PHP applications. The incident underscores the importance of proper validation of serialized objects and highlights the need for robust security practices in application development and deployment.