To ensure that the application is robust against all forms of input data, whether obtained from the user, infrastructure, external entities or database systems. This weakness leads to almost all of the major vulnerabilities in applications, such as Interpreter Injection, locale/Unicode attacks, file system attacks and buffer overflows.
All sections should be reviewed The most common web application security weakness is the failure to properly validate input from the client or environment.
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The Document Type Definition (DTD) language, which is native to the XML specification, is a schema language that is of relatively limited capability, but that also has other uses in XML aside from the expression of schemas.Two more expressive XML schema languages in widespread use are XML Schema (with a capital S) and RELAX NG.The mechanism for associating an XML document with a schema varies according to the schema language.For example, if you use HTML entity encoding on user input before it is sent to a browser, it will prevent most XSS attacks.However, simply preventing attacks is not enough - you must perform Intrusion Detection in your applications.