Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
Applications often need to transform data in and out of the XML format by using an XML parser. It may be possible for an attacker to inject data that may have an adverse effect on the XML parser when it is being processed. By nesting XML data and causing this data to be continuously self-referential, an attacker can cause the XML parser to consume more resources while processing, causing excessive memory consumption and CPU utilization. An attacker's goal is to leverage parser failure to his or her advantage. In most cases this type of an attack will result in a denial of service due to an application becoming unstable, freezing, or crash. However it may be possible to cause a crash resulting in arbitrary code execution, leading to a jump from the data plane to the control plane [R.230.1].
Skill or Knowledge Level: Low
Denial of service
Skill or Knowledge Level: High
Arbitrary code execution
Carefully validate and sanitize all user-controllable data prior to passing it to the XML parser routine. Ensure that the resultant data is safe to pass to the XML parser.
Perform validation on canonical data.
Pick a robust implementation of an XML parser.
Validate XML against a valid schema or DTD prior to parsing.
[R.230.1] [REF-43] Shlomo, Yona. "XML Parser Attacks: A summary of ways to attack an XML Parser". What is an XML Parser Attack?. 2007. <http://yeda.cs.technion.ac.il/~yona/talks/xml_parser_attacks/slides/slide2.html>.
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