CVE-2016-7478 in PHP
Summary
by MITRE
Zend/zend_exceptions.c in PHP, possibly 5.x before 5.6.28 and 7.x before 7.0.13, allows remote attackers to cause a denial of service (infinite loop) via a crafted Exception object in serialized data, a related issue to CVE-2015-8876.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2016-7478 represents a critical denial of service flaw within the PHP runtime environment, specifically affecting the zend_exceptions.c component that handles exception objects during serialization processes. This issue manifests when PHP applications process serialized data containing crafted Exception objects, creating a condition that leads to infinite loop execution. The vulnerability impacts PHP versions 5.x prior to 5.6.28 and 7.x prior to 7.0.13, making it a long-standing concern affecting multiple PHP release lines. The flaw operates through the deserialization mechanism where malformed Exception objects trigger recursive processing that never terminates, consuming system resources and rendering applications unavailable to legitimate users. This vulnerability is particularly dangerous because it can be exploited remotely through serialized data passed to PHP applications, often via HTTP parameters, cookies, or file uploads, making it a prime target for automated exploitation tools. The issue is categorized under CWE-400 as an Uncontrolled Resource Consumption vulnerability, specifically manifesting as an infinite loop that exhausts system processing power and memory resources. The operational impact extends beyond simple service disruption to include potential system instability, resource exhaustion, and cascading failures in web applications that rely on PHP for processing. This vulnerability directly aligns with ATT&CK technique T1499.004 for Network Denial of Service and T1595.001 for Remote Services, as it enables attackers to consume system resources remotely through crafted serialized data. The infinite loop condition occurs during the unserialization process when PHP attempts to reconstruct Exception objects, where the crafted data causes the deserialization engine to enter recursive processing that cannot be terminated naturally. This behavior creates a predictable resource exhaustion scenario that can be reliably exploited against vulnerable systems, making it particularly attractive to attackers seeking to disrupt services. The vulnerability shares similarities with CVE-2015-8876, indicating a pattern of serialization-related flaws in PHP's exception handling mechanisms that require careful validation of serialized input data. The flaw demonstrates the importance of input validation and proper resource management in serialization frameworks, as it shows how malformed data can cause legitimate processing functions to become infinite loops. Organizations running vulnerable PHP versions face significant risk of service disruption, with potential impacts including complete application unavailability, system crashes, and denial of service for legitimate users. The exploitation requires minimal technical expertise and can be automated, making it particularly dangerous in environments where PHP applications process untrusted data from external sources. Security professionals should prioritize patching affected systems immediately, as the vulnerability provides attackers with a straightforward method to cause system instability. The recommended mitigation strategy involves updating to PHP versions 5.6.28 or 7.0.13 and implementing proper input validation for serialized data, including sanitization of user-supplied serialized content and monitoring for unusual resource consumption patterns. Additional defensive measures include implementing web application firewalls to detect and block suspicious serialized data patterns and establishing robust application-level input validation to prevent malformed Exception objects from reaching the deserialization engine. The vulnerability underscores the critical need for secure coding practices in serialization frameworks and highlights the importance of proper error handling and resource management in language runtime environments.