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 supplying oversized payloads in input vectors that will be processed by the XML parser, an attacker can cause the XML parser to consume more resources while processing, causing excessive memory consumption and CPU utilization, and potentially cause execution of arbitrary code. An attacker's goal is to leverage parser failure to his or her advantage. In many cases this type of an attack will result in a denial of service due to an application becoming unstable, freezing, or crash. However it is possible to cause a crash resulting in arbitrary code execution, leading to a jump from the data plane to the control plane [R.231.1].
Skill or Knowledge Level: Low
Denial of service
Skill or Knowledge Level: High
Arbitrary code execution
Bad data is passed to the XML parser (possibly repeatedly), possibly making it crash or execute arbitrary code.
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.231.1] [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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