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Naziv
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XML Entity Expansion
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Sažetak
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An attacker submits an XML document to a target application where the XML document uses nested entity expansion to produce an excessively large output XML. XML allows the definition of macro-like structures that can be used to simplify the creation of complex structures. However, this capability can be abused to create excessive demands on a processor's CPU and memory. A small number of nested expansions can result in an exponential growth in demands on memory.
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Preduvjeti
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This type of attack requires that the target must receive XML input but either fail to provide an upper limit for entity expansion or provide a limit that is so large that it does not preclude significant resource consumption.
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Rješenja
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['Design: Use libraries and templates that minimize unfiltered input. Use methods that limit entity expansion and throw exceptions on attempted entity expansion.', 'Implementation: Disable altogether the use of inline DTD schemas in your XML parsing objects. If must use DTD, normalize, filter, use an allowlist and parse with methods and routines that will detect entity expansion from untrusted sources.']
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