CVE-2016-4463 in Xerces-C++
Summary
by MITRE
Stack-based buffer overflow in Apache Xerces-C++ before 3.1.4 allows context-dependent attackers to cause a denial of service via a deeply nested DTD.
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Analysis
by VulDB Data Team • 09/01/2022
The vulnerability identified as CVE-2016-4463 represents a critical stack-based buffer overflow within Apache Xerces-C++, a widely-used open-source XML parser library that processes structured data in numerous enterprise applications and web services. This flaw exists in versions prior to 3.1.4 and manifests when the parser encounters deeply nested Document Type Definitions within XML documents, creating a condition where the stack memory allocation becomes exhausted through recursive processing of nested elements. The vulnerability classifies under CWE-121 as a stack-based buffer overflow, where insufficient bounds checking allows attackers to overwrite adjacent stack memory locations, potentially leading to unpredictable application behavior or system compromise.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious XML document containing extremely deep nested DTD structures that trigger recursive parsing routines within the Xerces-C++ library. The parser's internal stack-based memory management fails to properly validate the depth of nesting, allowing recursive calls to accumulate until the stack overflows and causes the application to crash. This type of denial of service attack requires context-dependent conditions, meaning the attacker must have the ability to submit XML content to a system that processes such documents through the vulnerable Xerces-C++ parser implementation. The attack vector operates through the XML parsing subsystem, leveraging the library's recursive descent parsing algorithm that does not adequately enforce maximum nesting depth limits.
From an operational impact perspective, this vulnerability exposes systems that rely on Apache Xerces-C++ for XML processing to potential denial of service attacks, which can severely disrupt business operations and service availability. Applications affected include web servers, enterprise content management systems, database systems, and any software that processes XML data using the vulnerable library version. The vulnerability aligns with ATT&CK technique T1499.004 for resource exhaustion attacks, where attackers target parsing routines to consume excessive system resources and cause service disruption. Organizations running affected systems face significant risk of service degradation or complete application unavailability when processing malicious XML content, particularly in environments where XML processing is a core functionality component.
Mitigation strategies for CVE-2016-4463 primarily focus on upgrading to Apache Xerces-C++ version 3.1.4 or later, which includes fixed stack overflow protections and enhanced input validation mechanisms. Security administrators should implement comprehensive patch management procedures to ensure all affected systems receive timely updates, while also considering additional protective measures such as XML input sanitization, parsing depth limits, and monitoring for unusual parsing behavior. Organizations may also deploy application firewalls or XML gateways that can detect and block suspicious XML content patterns before they reach vulnerable applications. The vulnerability demonstrates the importance of proper input validation and memory management in parsing libraries, as highlighted by CWE-121 requirements for bounds checking and stack overflow prevention. Additionally, implementing runtime protections such as stack canaries or address space layout randomization may provide additional defense-in-depth measures against exploitation attempts.