Fixing SignedXml.CheckSignature for enveloped signature with #xpointer(/) Reference

This additionally improves support for URI-less Reference elements.

Co-authored-by: Samo Prelog <samo@prelog.io>
Co-authored-by: Kevin Jones <kevin@vcsjones.com>

Author: 3 people

src/libraries/System.Security.Cryptography.Xml/src/System.Security.Cryptography.Xml.csproj

@@ -4,6 +4,8 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <NoWarn>$(NoWarn);CA1850</NoWarn> <!-- CA1850 suppressed due to multitargeting -->
     <IsPackable>true</IsPackable>
+    <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
+    <ServicingVersion>1</ServicingVersion>
     <PackageDescription>Provides classes to support the creation and validation of XML digital signatures. The classes in this namespace implement the World Wide Web Consortium Recommendation, "XML-Signature Syntax and Processing", described at http://www.w3.org/TR/xmldsig-core/.
 
 Commonly Used Types:

src/libraries/System.Security.Cryptography.Xml/src/System/Security/Cryptography/Xml/Reference.cs

@@ -266,18 +266,31 @@ public void LoadXml(XmlElement value)
                         // let the transform read the children of the transformElement for data
                         transform.LoadInnerXml(transformElement.ChildNodes);
                         // Hack! this is done to get around the lack of here() function support in XPath
-                        if (transform is XmlDsigEnvelopedSignatureTransform
-                            && _uri != null && (_uri.Length == 0 || _uri[0] == '#'))
+                        if (transform is XmlDsigEnvelopedSignatureTransform)
                         {
                             // Walk back to the Signature tag. Find the nearest signature ancestor
                             // Signature-->SignedInfo-->Reference-->Transforms-->Transform
                             XmlNode? signatureTag = transformElement.SelectSingleNode("ancestor::ds:Signature[1]", nsm);
 
                             // Resolve the reference to get starting point for position calculation.
-                            XmlNode? referenceTarget =
-                                _uri.Length == 0
-                                ? transformElement.OwnerDocument
-                                : SignedXml!.GetIdElement(transformElement.OwnerDocument, Utils.GetIdFromLocalUri(_uri, out bool _));
+                            // This needs to match the way CalculateSignature resolves URI references.
+                            XmlNode? referenceTarget = null;
+                            if (_uri == null || _uri.Length == 0)
+                            {
+                                referenceTarget = transformElement.OwnerDocument;
+                            }
+                            else if (_uri[0] == '#')
+                            {
+                                string idref = Utils.ExtractIdFromLocalUri(_uri);
+                                if (idref == "xpointer(/)")
+                                {
+                                    referenceTarget = transformElement.OwnerDocument;
+                                }
+                                else
+                                {
+                                    referenceTarget = SignedXml!.GetIdElement(transformElement.OwnerDocument, idref);
+                                }
+                            }
 
                             XmlNodeList? signatureList = referenceTarget?.SelectNodes(".//ds:Signature", nsm);
                             if (signatureList != null)

src/libraries/System.Security.Cryptography.Xml/tests/SignedXmlTest.cs

@@ -9,6 +9,7 @@
 // (C) 2002, 2003 Motus Technologies Inc. (http://www.motus.com)
 // Copyright (C) 2004-2005, 2008 Novell, Inc (http://www.novell.com)
 
+using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
 using System.Net;
@@ -1993,5 +1994,45 @@ public void CheckSignatureHandlesIncorrectOrTamperedReferenceWithMultipleEnvelop
 
             Assert.False(subject.CheckSignature());
         }
+
+        public static object[][] EnvelopedSignatureWithRootXpointerReference = new object[][]
+        {
+            new object[] { true,  """<?xml version="1.0" encoding="UTF-8"?><hello><world>Hi</world><Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /><SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" /><Reference URI="#xpointer(/)"><Transforms><Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /><Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /></Transforms><DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" /><DigestValue>SVaCE5w9iLXTVYTKP1t/yjjmPXvWovMYpgljGgpgz2Y=</DigestValue></Reference></SignedInfo><SignatureValue>dqcBmS1ZvDJNhmCEgobpAb+A2XaiuB69dfGIhisZvqoxaWqAqv/0w49jp38+usJ5t3wcq3aMC631QE8iln+lHWrarojDMDWLa00isv3oE3q9UgOIV9e6MUSoRTTvQkmlK/LSYV9T/SKx6h03vLLcIkUMXaTkC/n2kthlJTGkLbU=</SignatureValue><KeyInfo><KeyValue><RSAKeyValue><Modulus>t6qV1iTlkCPoaIeOTvnDczQv5pytUxMoyNXws5vaMQYxfJMKos47dvmiLtfWUDLYXFX3Yf/JMC14plJw2JA5jLrlHLnZj/vCjRtXckmWW/wGYewXUqrgR1CytStUeQKj9mNsi76erukua10UhzIrWG+H6YQ/qS4AMMJZU6jBvO0=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue></KeyValue></KeyInfo></Signature></hello>""" },
+            new object[] { false, """<?xml version="1.0" encoding="UTF-8"?><hello>Tempered world<Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /><SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" /><Reference URI="#xpointer(/)"><Transforms><Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /><Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /></Transforms><DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" /><DigestValue>SVaCE5w9iLXTVYTKP1t/yjjmPXvWovMYpgljGgpgz2Y=</DigestValue></Reference></SignedInfo><SignatureValue>dqcBmS1ZvDJNhmCEgobpAb+A2XaiuB69dfGIhisZvqoxaWqAqv/0w49jp38+usJ5t3wcq3aMC631QE8iln+lHWrarojDMDWLa00isv3oE3q9UgOIV9e6MUSoRTTvQkmlK/LSYV9T/SKx6h03vLLcIkUMXaTkC/n2kthlJTGkLbU=</SignatureValue><KeyInfo><KeyValue><RSAKeyValue><Modulus>t6qV1iTlkCPoaIeOTvnDczQv5pytUxMoyNXws5vaMQYxfJMKos47dvmiLtfWUDLYXFX3Yf/JMC14plJw2JA5jLrlHLnZj/vCjRtXckmWW/wGYewXUqrgR1CytStUeQKj9mNsi76erukua10UhzIrWG+H6YQ/qS4AMMJZU6jBvO0=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue></KeyValue></KeyInfo></Signature></hello>""" },
+        };
+
+        [Theory]
+        [MemberData(nameof(EnvelopedSignatureWithRootXpointerReference))]
+        public void CheckSignatureHandlesEnvelopedSignatureWithRootXpointerReference(bool isValid, string xml)
+        {
+            XmlDocument xmlDoc = new ();
+            xmlDoc.LoadXml(xml);
+            SignedXml signedXml = new (xmlDoc);
+            signedXml.LoadXml(xmlDoc.GetElementsByTagName("Signature", SignedXml.XmlDsigNamespaceUrl)[0] as XmlElement);
+
+            Assert.Equal(isValid, signedXml.CheckSignature());
+        }
+
+
+        public static object[][] EnvelopedSignatureWithEmptyReference = new object[][]
+        {
+            new object[] { true,  """<?xml version="1.0" encoding="UTF-8"?><hello><world>Hi</world><Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /><SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" /><Reference><Transforms><Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /></Transforms><DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" /><DigestValue>SVaCE5w9iLXTVYTKP1t/yjjmPXvWovMYpgljGgpgz2Y=</DigestValue></Reference></SignedInfo><SignatureValue>CiB9jgIS7+Wq+lpyzCGsBZQcQ2BxqQuEU9VCvb3Li5jMtjwRV1bMO+4Wfnb4VWhEtEUq6NdiVGXhC1xvtVLnnLDX7CD/jG6NvM1Yd0/rf0UUceBhzYLFE9HLsopsBmmm3t8FO6ZtRr1QqKM0XDaQleGK9vYd2m2Jq8OR3r/w4OY=</SignatureValue><KeyInfo><KeyValue><RSAKeyValue><Modulus>vcM1wQVmLB9DwdnAym8l8nw63/HlTVzgTDhIwNzWPhsPE/qr2wlK4TEQ3rjU+RAdNytfFNCnuuh75ZVMjAWCV9h6VDlp0DOvBhb6GenhymtTAdJJKzBXKJP6mNPga9cPOP31IZ36Ui00G3fjBBPrHa7nStludgL9Wi0dBU28DjU=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue></KeyValue></KeyInfo></Signature></hello>""" },
+            new object[] { false, """<?xml version="1.0" encoding="UTF-8"?><hello><WORLD>HI</WORLD><Signature xmlns="http://www.w3.org/2000/09/xmldsig#"><SignedInfo><CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#WithComments" /><SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" /><Reference><Transforms><Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" /></Transforms><DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" /><DigestValue>SVaCE5w9iLXTVYTKP1t/yjjmPXvWovMYpgljGgpgz2Y=</DigestValue></Reference></SignedInfo><SignatureValue>CiB9jgIS7+Wq+lpyzCGsBZQcQ2BxqQuEU9VCvb3Li5jMtjwRV1bMO+4Wfnb4VWhEtEUq6NdiVGXhC1xvtVLnnLDX7CD/jG6NvM1Yd0/rf0UUceBhzYLFE9HLsopsBmmm3t8FO6ZtRr1QqKM0XDaQleGK9vYd2m2Jq8OR3r/w4OY=</SignatureValue><KeyInfo><KeyValue><RSAKeyValue><Modulus>vcM1wQVmLB9DwdnAym8l8nw63/HlTVzgTDhIwNzWPhsPE/qr2wlK4TEQ3rjU+RAdNytfFNCnuuh75ZVMjAWCV9h6VDlp0DOvBhb6GenhymtTAdJJKzBXKJP6mNPga9cPOP31IZ36Ui00G3fjBBPrHa7nStludgL9Wi0dBU28DjU=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue></KeyValue></KeyInfo></Signature></hello>""" },
+        };
+
+        [Theory]
+        [MemberData(nameof(EnvelopedSignatureWithEmptyReference))]
+        public void CheckSignatureHandlesEnvelopedSignatureWithEmptyReference(bool isValid, string xml)
+        {
+            XmlDocument xmlDoc = new ();
+            xmlDoc.LoadXml(xml);
+            SignedXml signedXml = new (xmlDoc);
+            signedXml.LoadXml(xmlDoc.GetElementsByTagName("Signature", SignedXml.XmlDsigNamespaceUrl)[0] as XmlElement);
+
+            // without this, CheckSignature throws
+            ((Reference)signedXml.SignedInfo.References[0]).TransformChain[0].LoadInput(xmlDoc);
+
+            Assert.Equal(isValid, signedXml.CheckSignature());
+        }
     }
 }