CVE-2016-7131 in PHP
Summary
by MITRE
ext/wddx/wddx.c in PHP before 5.6.25 and 7.x before 7.0.10 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) or possibly have unspecified other impact via a malformed wddxPacket XML document that is mishandled in a wddx_deserialize call, as demonstrated by a tag that lacks a < (less than) character.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-7131 represents a critical NULL pointer dereference issue within PHP's WDDX (Web Distributed Data Exchange) extension, affecting versions prior to 5.6.25 and 7.0.10. This flaw resides in the ext/wddx/wddx.c source file and specifically impacts the wddx_deserialize function which processes WDDX packet XML documents. The vulnerability manifests when PHP encounters malformed WDDX XML structures that lack proper XML tag formatting, particularly when a tag is missing the opening less than character. This fundamental parsing error creates a condition where the application attempts to dereference a NULL pointer during the deserialization process, leading to immediate application termination and denial of service conditions.
The technical exploitation of this vulnerability occurs through the manipulation of WDDX XML packet structures that are processed by PHP's wddx_deserialize function. When an attacker crafts a malicious XML document containing improperly formatted tags that lack the required opening bracket character, the WDDX parser fails to properly validate the input structure. This parsing failure results in the application attempting to access memory locations that have not been properly initialized or allocated, causing the NULL pointer dereference. The vulnerability is classified under CWE-476 as a NULL Pointer Dereference, which is a common class of software defects that can lead to application crashes and potentially more severe consequences depending on the execution environment. The flaw demonstrates poor input validation and error handling practices within PHP's XML processing subsystem.
From an operational perspective, this vulnerability presents significant risk to web applications that utilize PHP's WDDX functionality for data exchange or serialization purposes. The impact extends beyond simple denial of service as the vulnerability could potentially be leveraged for more sophisticated attacks depending on the system configuration and execution context. When exploited, the vulnerability causes immediate application crashes, disrupting service availability for legitimate users and potentially providing attackers with information about the underlying system configuration. The vulnerability is particularly concerning because WDDX deserialization is often used in web applications for processing data from external sources, making it a potential vector for remote exploitation. The ATT&CK framework categorizes this as a Denial of Service attack technique under the T1499.004 category, which involves exploitation of software vulnerabilities to disrupt system availability.
The mitigation strategy for CVE-2016-7131 centers on immediate version upgrades to PHP 5.6.25 or 7.0.10 and later releases where the vulnerability has been patched. Organizations should also implement proper input validation and sanitization measures for all XML processing functions, particularly when handling external or user-provided data. Network-level protections such as XML parsers with strict validation and content filtering can help reduce the attack surface. Additionally, implementing proper error handling and recovery mechanisms within applications that utilize WDDX functionality can help prevent complete application crashes. Security monitoring should include detection of unusual XML processing patterns and potential exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date software versions and proper input validation practices in preventing remote code execution and denial of service attacks. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability class.