CVE-2017-9119 in PHP
Summary
by MITRE
The i_zval_ptr_dtor function in Zend/zend_variables.h in PHP 7.1.5 allows attackers to cause a denial of service (memory consumption and application crash) or possibly have unspecified other impact by triggering crafted operations on array data structures.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-9119 resides within the i_zval_ptr_dtor function located in Zend/zend_variables.h of PHP version 7.1.5, representing a critical memory management flaw that can be exploited to execute denial of service attacks or potentially achieve other unspecified impacts. This vulnerability specifically targets the handling of array data structures during variable destruction processes, where improper memory management leads to unpredictable behavior. The flaw occurs when crafted array operations trigger the destructor function, causing excessive memory consumption or application crashes that can render the affected PHP application unavailable to legitimate users. The vulnerability is categorized under CWE-401 as a weakness related to improper handling of memory allocation and deallocation, which directly impacts the stability and availability of web applications built on PHP.
The technical implementation of this vulnerability stems from the improper handling of reference counting and memory deallocation within PHP's Zend Engine's variable management system. When arrays containing specific reference patterns are processed through the i_zval_ptr_dtor function, the memory management routines fail to properly account for circular references or complex nested structures, leading to memory leaks or stack corruption. Attackers can construct malicious array structures that, when processed by the affected PHP version, cause the destructor to enter infinite loops or consume excessive memory resources. This behavior aligns with ATT&CK technique T1499.004 for resource exhaustion attacks, where adversaries leverage application vulnerabilities to consume system resources and cause service disruption. The vulnerability's exploitation requires understanding of PHP's internal memory management mechanisms and the ability to craft specific array data structures that trigger the problematic code path.
The operational impact of CVE-2017-9119 extends beyond simple denial of service, as it can potentially enable more sophisticated attacks depending on the application environment and execution context. Applications that process user-supplied array data without proper sanitization become vulnerable to this attack vector, making web applications particularly susceptible. When exploited successfully, the vulnerability can cause complete application crashes, leading to service unavailability for legitimate users, or in some cases, may allow for more advanced exploitation techniques if the application environment provides additional attack surface. The memory consumption patterns associated with this vulnerability can also lead to system-wide performance degradation, affecting not only the targeted PHP application but potentially other services running on the same system. Organizations running PHP 7.1.5 applications should consider this vulnerability as a critical threat to their operational continuity and security posture.
Mitigation strategies for CVE-2017-9119 primarily focus on immediate software updates and application-level protections. The most effective solution involves upgrading to PHP 7.1.6 or later versions where the vulnerability has been patched through improved memory management routines and proper reference counting mechanisms. System administrators should implement comprehensive patch management procedures to ensure all PHP installations are updated promptly. Additionally, applications should implement input validation and sanitization measures to prevent malicious array structures from reaching the vulnerable code paths. Security monitoring should be enhanced to detect unusual memory consumption patterns or application crashes that may indicate exploitation attempts. Organizations should also consider implementing application firewalls or web application firewalls that can detect and block suspicious array data patterns. The vulnerability's remediation aligns with industry best practices for vulnerability management and software security maintenance, emphasizing the importance of keeping software components up to date with the latest security patches.