CVE-2008-4482 in Xerces-C++
Summary
by MITRE
The XML parser in Xerces-C++ before 3.0.0 allows context-dependent attackers to cause a denial of service (stack consumption and crash) via an XML schema definition with a large maxOccurs value, which triggers excessive memory consumption during validation of an XML file.
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Analysis
by VulDB Data Team • 08/30/2019
The vulnerability identified as CVE-2008-4482 represents a critical denial of service flaw within the Xerces-C++ XML parser library, specifically affecting versions prior to 3.0.0. This issue arises from inadequate input validation mechanisms within the parser's handling of XML schema definitions, creating a scenario where maliciously crafted XML documents can trigger excessive resource consumption. The vulnerability operates through a context-dependent attack vector where an attacker must construct an XML schema with an extremely large maxOccurs value to exploit the weakness, making it particularly dangerous in environments where XML validation is performed on untrusted input data. The flaw directly impacts the parser's ability to manage memory allocation during schema validation processes, leading to system instability and potential service disruption.
The technical root cause of this vulnerability stems from the parser's insufficient bounds checking when processing XML schema elements, particularly the maxOccurs attribute which defines the maximum number of times an element may occur within a schema. When an attacker provides an XML schema definition containing an excessively large maxOccurs value, the parser attempts to allocate memory proportional to this value during validation, resulting in rapid stack consumption and eventual system crash. This behavior aligns with CWE-770, which categorizes inadequate resource allocation as a fundamental weakness in software design. The vulnerability operates at the intersection of memory management and input validation, where the parser fails to implement proper safeguards against pathological input values that could lead to resource exhaustion.
The operational impact of CVE-2008-4482 extends beyond simple service disruption to encompass broader security implications for systems relying on Xerces-C++ for XML processing. Attackers can exploit this vulnerability to consume system resources rapidly, potentially leading to complete system crashes or denial of service conditions that affect legitimate users. The vulnerability is particularly concerning in web applications, enterprise systems, and any environment where XML validation occurs on user-submitted content, as it can be leveraged to create sustained denial of service attacks. From an adversarial perspective, this flaw maps to ATT&CK technique T1499.004, which describes the use of resource exhaustion attacks to disrupt services, making it a valuable target for threat actors seeking to compromise system availability.
Mitigation strategies for this vulnerability primarily focus on immediate version upgrades to Xerces-C++ 3.0.0 or later, which contain the necessary fixes to properly handle large maxOccurs values and prevent excessive memory consumption. Organizations should also implement input validation measures to screen XML schemas for potentially malicious values before processing, though this approach provides only partial protection given the nature of the vulnerability. Additionally, system administrators should consider implementing resource limits and monitoring mechanisms to detect and respond to abnormal memory consumption patterns that may indicate exploitation attempts. The fix implemented in newer versions addresses the core issue by introducing proper bounds checking and memory allocation controls, preventing the parser from allocating excessive resources during schema validation operations and ensuring system stability under adversarial conditions.