CVE-2013-4113 in PHP
Summary
by MITRE
ext/xml/xml.c in PHP before 5.3.27 does not properly consider parsing depth, which allows remote attackers to cause a denial of service (heap memory corruption) or possibly have unspecified other impact via a crafted document that is processed by the xml_parse_into_struct function.
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Analysis
by VulDB Data Team • 05/18/2021
The vulnerability identified as CVE-2013-4113 represents a critical heap memory corruption issue within PHP's XML parsing functionality, specifically affecting versions prior to 5.3.27. This flaw resides in the ext/xml/xml.c file and fundamentally stems from inadequate handling of XML parsing depth limits during document processing. The vulnerability manifests when the xml_parse_into_struct function processes maliciously crafted XML documents that exceed normal parsing depth parameters, creating conditions where heap memory can be corrupted through improper memory allocation and deallocation sequences.
The technical implementation of this vulnerability exploits the lack of proper depth validation mechanisms within PHP's XML parser implementation. When an attacker submits a specially constructed XML document containing excessive nested elements or recursive structures, the parser fails to enforce appropriate depth limits that would normally prevent such excessive parsing operations. This absence of depth checking allows the parser to continue processing beyond reasonable memory constraints, leading to heap corruption that can result in application crashes or potentially more severe consequences including arbitrary code execution. The flaw operates at the core level of PHP's XML processing engine, making it particularly dangerous as it affects fundamental parsing operations used throughout web applications.
From an operational impact perspective, this vulnerability creates significant risks for web applications that rely on XML processing, particularly those that accept user input through XML data feeds or API endpoints. The denial of service condition can render web applications completely unavailable, causing business disruption and potential financial losses. Additionally, the unspecified other impacts mentioned in the vulnerability description suggest that under certain conditions, attackers might be able to leverage this heap corruption for more sophisticated attacks beyond simple service disruption. The vulnerability affects a wide range of applications since XML parsing is a common operation in web development, making it a prime target for exploitation.
The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and relates to ATT&CK technique T1203, which covers exploitation of memory corruption vulnerabilities. Organizations should implement immediate mitigations including upgrading to PHP 5.3.27 or later versions where the parsing depth limitations have been properly enforced. Additional protective measures include implementing XML parsing depth limits at the application level, validating all XML input through strict schema validation, and employing web application firewalls that can detect and block suspicious XML parsing patterns. Regular security assessments should be conducted to ensure that no legacy applications remain vulnerable, and proper input sanitization practices should be enforced throughout the development lifecycle to prevent similar issues from occurring in custom XML processing implementations.