CVE-2026-102495 in XmlSchema
Summary
by MITRE • 09/29/2026
Apache XmlSchema doesn't limit how deeply schema imports and includes can be nested, 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 limitation on the depth of nested schema imports and includes within XML Schema Definition files. When processing these schemas, the library recursively resolves dependencies by importing or including other schema documents without enforcing a maximum recursion limit. This architectural oversight allows a malicious actor to construct a specially crafted XML schema that contains deeply nested references to itself or circular dependency chains. As the parser attempts to resolve each layer of imports and includes, it consumes stack space for each recursive call until the system's available memory is exhausted.
This uncontrolled recursion directly leads to a stack overflow condition, resulting in an application crash or hang. The primary operational impact is a denial of service against any system relying on Apache XmlSchema for XML validation or processing. Attackers can exploit this flaw by submitting maliciously structured schema documents through APIs that accept such inputs, effectively disrupting service availability without requiring authentication or elevated privileges if the input source is untrusted. This type of vulnerability aligns with CWE-675, which describes operations with duplicate resources, specifically excessive resource consumption due to recursive processing loops.
From a threat modeling perspective using the MITRE ATT&CK framework, this flaw facilitates Resource Hijacking under the T1496 category, where an attacker consumes computational resources to degrade service quality or cause outages. It also relates to CWE-787, as stack overflows can potentially lead to arbitrary code execution in lower-level languages if not properly contained by modern runtime protections, although the primary reported impact here is denial of service due to resource exhaustion. The lack of depth checking represents a fundamental input validation failure where the structural complexity of the XML schema is treated as trusted and bounded without verification against system limits.
To mitigate this vulnerability, organizations must upgrade Apache XmlSchema to version 2.3.3 or later, which implements proper bounds checking for recursive schema resolution operations. For systems that cannot immediately patch due to dependency constraints, implementing a wrapper around the parser with explicit recursion depth counters can provide temporary protection by throwing an exception when a predefined threshold is reached. Additionally, input validation strategies should be employed at the application boundary to reject XML schemas that exhibit signs of excessive nesting or circular references before they reach the parsing engine. Regular security audits and static code analysis tools configured to detect unbounded recursive calls are recommended practices to prevent similar issues in future development cycles.