The software accepts XML from an untrusted source but does not validate the XML against the proper schema.
Most successful attacks begin with a violation of the programmer's assumptions. By accepting an XML document without validating it against a DTD or XML schema, the programmer leaves a door open for attackers to provide unexpected, unreasonable, or malicious input.
Time of Introduction
Technical Impact: Unexpected state
The following code loads an XML file without validating it against a
known XML Schema or DTD.
Always validate XML input against a known XML Schema or DTD.
It is not possible for an XML parser to validate all aspects of a
document's content because a parser cannot understand the complete
semantics of the data. However, a parser can do a complete and thorough
job of checking the document's structure and therefore guarantee to the
code that processes the document that the content is well-formed.
the weakness exists independent of other weaknesses)