CVE-2026-102496 in XmlSchema
Summary
by MITRE • 09/29/2026
Apache XmlSchema doesn't limit how deeply schema structures can be nested when it builds its schema model, so a malicious schema can make parsing recurse until the stack overflows. This causes a denial of service. Users are recommended to upgrade to version 2.3.3, which fixes this issue.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability in Apache XmlSchema stems from an insufficient validation mechanism regarding the depth of nested structures within XML Schema Definition files. When the library processes a schema document, it constructs an internal model by recursively parsing and validating the hierarchical relationships between elements, types, and complex definitions. The core technical flaw lies in the absence of a configurable or hard-coded limit on recursion depth during this construction phase. Consequently, if an attacker provides a maliciously crafted XML Schema with deeply nested structures, such as circular references or excessively deep inheritance chains that do not terminate within reasonable bounds, the parser will continue to recurse indefinitely until it exhausts the available stack space allocated by the operating system and Java Virtual Machine.
This uncontrolled recursion directly leads to a StackOverflowError in the Java runtime environment, which typically results in the abrupt termination of the application thread or process handling the request. From an operational perspective, this constitutes a classic denial of service vulnerability where availability is compromised without requiring authentication or privilege escalation. An attacker can exploit this by submitting specially crafted XML Schema documents through any interface that accepts schema definitions for validation or processing, such as web services endpoints, configuration upload mechanisms, or data ingestion pipelines that rely on Apache XmlSchema for structural integrity checks. The impact ranges from temporary service disruption due to thread crashes to complete application unavailability if the underlying server process fails and cannot recover automatically.
In terms of industry classification standards, this vulnerability aligns with CWE-675, which describes operations with duplicate or redundant inputs that lead to resource exhaustion, specifically manifesting here as a stack overflow due to excessive recursion depth. It also relates closely to CWE-400, concerning uncontrolled resource consumption, where the system fails to limit the amount of resources used by an attacker-controlled input. Within the MITRE ATT&CK framework, this exploitation technique falls under T1499, Endpoint Denial of Service, specifically utilizing methodical exhaustion or overflow techniques against application services rather than network bandwidth saturation.
To mitigate this risk, organizations must prioritize upgrading to Apache XmlSchema version 2.3.3 or later, as the maintainers have implemented safeguards to limit recursion depth and prevent stack overflows during schema model construction. For environments where immediate patching is not feasible, defensive measures should include implementing strict input validation at the network perimeter using Web Application Firewalls configured to detect excessively deep XML structures or recursive patterns in uploaded files. Additionally, application-level mitigations can involve configuring JVM parameters such as -Xss to increase stack size temporarily, though this only delays rather than prevents exploitation and is not a recommended long-term solution. Developers should also review any custom code that utilizes the library to ensure no workarounds bypass the internal depth checks introduced in the patched versions.