|Summary ||XML Denial of Service (XDoS) can be applied to any technology that utilizes XML data. This is, of course, most distributed systems technology including Java, .Net, databases, and so on. XDoS is most closely associated with web services, SOAP, and Rest, because remote service requesters can post malicious XML payloads to the service provider designed to exhaust the service provider's memory, CPU, and/or disk space. The main weakness in XDoS is that the service provider generally must inspect, parse, and validate the XML messages to determine routing, workflow, security considerations, and so on. It is exactly these inspection, parsing, and validation routines that XDoS targets.
There are three primary attack vectors that XDoS can navigate
Target CPU through recursion: attacker creates a recursive payload and sends to service provider
Target memory through jumbo payloads: service provider uses DOM to parse XML. DOM creates in memory representation of XML document, but when document is very large (for example, north of 1 Gb) service provider host may exhaust memory trying to build memory objects.
XML Ping of death: attack service provider with numerous small files that clog the system.
All of the above attacks exploit the loosely coupled nature of web services, where the service provider has little to no control over the service requester and any messages the service requester sends. |