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XmlSecureResolver Class

Helps to secure another implementation of XmlResolver by wrapping the XmlResolver object and restricting the resources that the underlying XmlResolver has access to.

System.Object
  System.Xml.XmlResolver
    System.Xml.XmlSecureResolver

Namespace:  System.Xml
Assembly:  System.Xml (in System.Xml.dll)

[PermissionSetAttribute(SecurityAction.InheritanceDemand, Name = "FullTrust")]
[PermissionSetAttribute(SecurityAction.InheritanceDemand, Name = "FullTrust")]
public class XmlSecureResolver : XmlResolver

The XmlSecureResolver type exposes the following members.

  NameDescription
Public methodXmlSecureResolver(XmlResolver, PermissionSet)Initializes a new instance of the XmlSecureResolver class with the XmlResolver and PermissionSet specified.
Public methodXmlSecureResolver(XmlResolver, Evidence)Initializes a new instance of the XmlSecureResolver class with the XmlResolver and System.Security.Policy.Evidence specified.
Public methodXmlSecureResolver(XmlResolver, String)Initializes a new instance of the XmlSecureResolver class with the XmlResolver and URL provided.
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  NameDescription
Public propertyCredentialsSets credentials used to authenticate web requests. (Overrides XmlResolver.Credentials.)
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  NameDescription
Public methodStatic memberCreateEvidenceForUrlCreates evidence using the supplied URL.
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetEntityMaps a URI to an object that contains the actual resource. This method temporarily sets the System.Security.PermissionSet created in the constructor by calling PermissionSet.PermitOnly before calling GetEntity on the underlying XmlResolver to open the resource. (Overrides XmlResolver.GetEntity(Uri, String, Type).)
Public methodGetEntityAsyncAsynchronously maps a URI to an object that contains the actual resource. (Overrides XmlResolver.GetEntityAsync(Uri, String, Type).)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodResolveUriResolves the absolute URI from the base and relative URIs by calling ResolveUri on the underlying XmlResolver. (Overrides XmlResolver.ResolveUri(Uri, String).)
Public methodSupportsTypeEnables the resolver to return types other than System.IO.Stream. (Inherited from XmlResolver.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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The XmlUrlResolver class is the default resolver for all classes in the System.Xml namespace. It is used to load XML documents and to resolve external resources such as entities, DTDs or schemas, and import or include directives.

You can override this default by specifying the XmlResolver object to use. For example, if you want to restrict the resources that the underlying XmlResolver can access, you can use an XmlSecureResolver object.

XmlSecureResolver wraps around a concrete implementation of XmlResolver and restricts the resources that the underlying XmlResolver has access to. For example, XmlSecureResolver has the ability to prohibit cross-domain redirection, which occurs from an embedded Uniform Resource Identifier (URI) reference.

When you construct an XmlSecureResolver object, you provide a valid XmlResolver implementation along with a URL, an instance of an evidence object, or a permission set, which is used by the XmlSecureResolver to determine security. Either a System.Security.PermissionSet is generated or the existing one is used and PermissionSet.PermitOnly is called on it to help secure the underlying XmlResolver.

Security noteSecurity Note

XmlSecureResolver objects can contain sensitive information such as user credentials. You should be careful when caching XmlSecureResolver objects and should not pass the XmlSecureResolver object to an untrusted component.

Important noteImportant

There are differences in the security infrastructure for code running on the .NET Framework common language runtime (CLR) and for code running on the CLR that is integrated within Microsoft SQL Server 2005. This can lead to cases where code developed for the .NET Framework CLR operates differently when used on the SQL Server integrated CLR. One of these differences affects the XmlSecureResolver class when you have evidence that is based on a URL (that is, when you use the CreateEvidenceForUrl(String) method or the XmlSecureResolver constructor). The policy resolution mechanism of the SQL Server integrated CLR does not use the Url or Zone information. Instead, it grants permissions based on the GUID that the server adds when assemblies are loaded. When you use the XmlSecureResolver in the SQL Server integrated CLR, provide any required evidence directly by using a specified PermissionSet.

To use a secure resolver

  1. Create an XmlSecureResolver with the correct permission set.

  2. Create an XmlReaderSettings object that uses the XmlSecureResolver object.

    XmlReaderSettings settings = new XmlReaderSettings();
    settings.XmlResolver = myResolver;
    
  3. Pass the XmlReaderSettings object to the Create method when you're creating the XmlReader object.

    XmlReader reader = XmlReader.Create("books.xml", settings);
    

To restrict access by using a URL

Use the XmlSecureResolver(XmlResolver, String) constructor to create an XmlSecureResolver object that is allowed to access your local intranet site only.

XmlSecureResolver myResolver = new XmlSecureResolver(new XmlUrlResolver(), "http://myLocalSite/");

To restrict access by using a permission set

  1. Create a WebPermission object.

    WebPermission myWebPermission = new WebPermission(PermissionState.None);
    
  2. Specify the URLs that you want to allow access to.

    myWebPermission.AddPermission(NetworkAccess.Connect,"http://www.contoso.com/");
    myWebPermission.AddPermission(NetworkAccess.Connect,"http://litwareinc.com/data/");
    
  3. Add the web permissions to the PermissionSet object.

    PermissionSet myPermissions = new PermissionSet(PermissionState.None);
    myPermissions.AddPermission(myWebPermission);
    
  4. Use the XmlSecureResolver(XmlResolver, PermissionSet) constructor to create an XmlSecureResolver object by using the permission set.

    XmlSecureResolver myResolver = new XmlSecureResolver(new XmlUrlResolver(), myPermissions);
    

    See the XmlSecureResolver reference page for another example.

To restrict access by using evidence

You can restrict access by using the XmlSecureResolver(XmlResolver, Evidence) constructor and specifying Evidence. The Evidence is used to create the PermissionSet that is applied to the underlying XmlResolver. The XmlSecureResolver calls PermitOnly on the created PermissionSet before opening any resources.

Here are some common scenarios and the type of evidence to provide for each:

  • If you are working in a fully trusted environment, use your assembly to create the evidence:

    Evidence myEvidence = this.GetType().Assembly.Evidence;
    XmlSecureResolver myResolver;
    myResolver = new XmlSecureResolver(new XmlUrlResolver(), myEvidence);
    
  • If you are working in a semi-trusted environment, you have code or data coming from an outside source, and you know the origin of the outside source and have a verifiable URI, use the URI to create the evidence:

    
    Evidence myEvidence = XmlSecureResolver.CreateEvidenceForUrl(sourceURI);
    XmlSecureResolver myResolver = new XmlSecureResolver(new XmlUrlResolver(), myEvidence);
    
  • If you are working in a semi-trusted environment and you have code or data coming from an outside source, but you don't know the origin of the outside source, either:

    Set the evidence parameter to null. This allows no access to resources.

    -or-

    If your application requires some access to resources, request evidence from the caller.

To use the secure resolver to load an XSLT style sheet

  1. Create an XmlSecureResolver with the correct permission set.

  2. Pass the XmlSecureResolver to the Load method.

    XslCompiledTransform xslt = new XslCompiledTransform();
    xslt.Load("http://serverName/data/xsl/sort.xsl", null, myResolver);
    

Notes to Inheritors

This class has an inheritance demand. Full trust is required to inherit from the XmlSecureResolver class. See Inheritance Demands for more information.

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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