CA5370: Use XmlReader for validating reader

Cause

Validating untrusted XML input with the XmlValidatingReader class instantiated without an XmlReader object can potentially lead to denial of service, information disclosure, and server-side request forgery. These attacks are enabled by untrusted DTD and XML schema processing, which allows for the inclusion of XML bombs and malicious external entities in the XML. Only with XmlReader is it possible to disable DTD. Inline XML schema processing as XmlReader has the ProhibitDtd and ProcessInlineSchema property set to false by default in .NET Framework starting in version 4.0.

Rule description

Processing untrusted DTD and XML schemas may enable loading dangerous external references. This dangerous loading can be restricted by using an XmlReader with a secure resolver or with DTD and XML inline schema processing disabled. This rule detects code that uses the XmlValidatingReader class without XmlReader as a constructor parameter.

How to fix violations

• Use XmlValidatingReader(XmlReader) with ProhibitDtd and ProcessInlineSchema properties set to false.
• Starting in .NET Framework 2.0, XmlValidatingReader is considered obsolete. You can instantiate a validating reader with XmlReader.Create.

When to suppress warnings

You can potentially suppress this warning if the XmlValidatingReader is always used to validate XML that comes from a trusted source and hence cannot be tampered with.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA5370
// The code that's violating the rule is on this line.
#pragma warning restore CA5370

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA5370.severity = none

For more information, see How to suppress code analysis warnings.

Pseudo-code examples

Violation

The following pseudo-code sample illustrates the pattern detected by this rule. The type of the first parameter of XmlValidatingReader.XmlValidatingReader() is not XmlReader.

using System;
using System.IO;
using System.Xml;
...
public void TestMethod(Stream xmlFragment, XmlNodeType fragType, XmlParserContext context)
{
    var obj = new XmlValidatingReader(xmlFragment, fragType, context);
}

Solution

using System;
using System.Xml;
...
public void TestMethod(XmlReader xmlReader)
{
    var obj = new XmlValidatingReader(xmlReader);
}