CVE-2016-9934 in macOS
Summary
by MITRE
ext/wddx/wddx.c in PHP before 5.6.28 and 7.x before 7.0.13 allows remote attackers to cause a denial of service (NULL pointer dereference) via crafted serialized data in a wddxPacket XML document, as demonstrated by a PDORow string.
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Analysis
by VulDB Data Team • 11/03/2022
The vulnerability identified as CVE-2016-9934 represents a critical denial of service flaw within the PHP web application scripting language. This issue specifically affects the WDDX (Web Distributed Data Exchange) extension functionality, which is used for serializing and deserializing data structures in XML format. The vulnerability exists in PHP versions prior to 5.6.28 and 7.x versions prior to 7.0.13, making it a widespread concern across multiple PHP release branches. The flaw manifests when PHP processes crafted serialized data contained within a wddxPacket XML document, creating a scenario where malicious input can trigger system instability.
The technical mechanism behind this vulnerability involves a NULL pointer dereference condition that occurs during the deserialization process of WDDX data structures. When PHP encounters a malformed wddxPacket XML document containing specifically crafted PDORow string data, the internal parsing routines fail to properly validate the structure before attempting to access memory locations. This leads to a situation where the application attempts to dereference a null pointer, causing an immediate crash or termination of the PHP process. The vulnerability is particularly dangerous because it can be triggered through standard PHP serialization mechanisms, making it accessible to attackers who can submit malicious data through web forms, API endpoints, or any input method that processes WDDX serialized data.
The operational impact of CVE-2016-9934 extends beyond simple service disruption, as it can be exploited to create persistent denial of service conditions that may require manual intervention to resolve. Attackers can repeatedly submit malicious WDDX data to web applications that utilize PHP's WDDX extension, causing continuous process crashes and system unavailability. This vulnerability aligns with CWE-476 which categorizes NULL pointer dereference conditions as a fundamental programming error that can lead to system instability. The attack vector is particularly concerning because it requires minimal privileges and can be executed through standard web application interaction patterns, making it a preferred target for automated exploitation tools.
The security implications of this vulnerability are significant for web application environments that rely on PHP processing WDDX serialized data. Organizations running affected PHP versions face potential service interruptions that can impact user access and application availability. The vulnerability demonstrates the importance of proper input validation and error handling in serialization libraries, as highlighted by ATT&CK technique T1499 which covers denial of service attacks. Mitigation strategies should include immediate patching of PHP installations to versions 5.6.28 or 7.0.13 and higher, along with implementing additional input validation measures for any WDDX data processing components. Security teams should also consider monitoring for unusual patterns of WDDX data processing and implementing application-level firewalls to detect and block malicious serialized data attempts. The vulnerability underscores the critical need for regular security updates and the importance of maintaining current software versions to protect against known exploits that can compromise system availability and stability.