CVE-2016-7132 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 an invalid wddxPacket XML document that is mishandled in a wddx_deserialize call, as demonstrated by a stray element inside a boolean element, leading to incorrect pop processing.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-7132 represents a critical denial of service weakness in PHP's WDDX (Web Distributed Data Exchange) processing functionality. This flaw exists in PHP versions prior to 5.6.25 and 7.x versions prior to 7.0.10, where the ext/wddx/wddx.c module fails to properly validate malformed XML documents during deserialization processes. The vulnerability specifically manifests when the wddx_deserialize function encounters an invalid wddxPacket XML structure, particularly when stray elements appear within boolean elements, causing the application to crash due to improper pop processing operations.
The technical root cause of this vulnerability stems from inadequate input validation within the WDDX deserialization routine. When PHP processes a malformed wddxPacket XML document containing unexpected elements within boolean containers, the internal stack management mechanism becomes corrupted during the parsing sequence. This improper handling leads to a NULL pointer dereference condition, where the application attempts to access memory at address zero, resulting in an immediate application crash. The vulnerability operates at the level of XML parsing and stack manipulation, making it particularly dangerous as it can be triggered through simple malformed XML input without requiring any special privileges or complex attack vectors.
From an operational perspective, this vulnerability presents significant risks to web applications that rely on PHP's WDDX functionality for data exchange and serialization. Attackers can exploit this weakness by sending specially crafted XML documents to applications using wddx_deserialize, causing service disruption and potential denial of service conditions. The impact extends beyond simple availability issues, as the crash can potentially expose underlying system instability or create conditions that might allow for further exploitation. This vulnerability particularly affects applications that process external XML data from untrusted sources, making it a prime target for automated scanning and exploitation campaigns. The flaw's potential for unspecified other impacts suggests that under certain conditions, it might provide opportunities for additional security consequences beyond simple service disruption.
The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and relates to ATT&CK technique T1499.004 for denial of service through resource consumption. Organizations should prioritize immediate patching of affected PHP installations to address this vulnerability. Mitigation strategies include implementing strict input validation for all XML data processed through WDDX functions, disabling WDDX functionality when not required, and employing web application firewalls to filter malformed XML traffic. Additionally, application developers should consider using alternative serialization methods that do not rely on vulnerable XML parsing libraries, and implement proper error handling and monitoring to detect exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any other potentially affected components within the application stack that might utilize similar parsing mechanisms.