dotnet/wpf · error · XmlException

SR.RequiredXmlAttributeMissing (uri)

Error message

SR.RequiredXmlAttributeMissing (uri)

What it means

ParsePartUri failed to extract a valid part URI from the signature manifest, so the required URI attribute (per the OPC/XMLDSig manifest schema) is missing. The library throws because every Reference entry in a package signature must carry a Uri attribute identifying the signed part; without it the manifest is structurally invalid and cannot be verified.

Solutions

  1. Inspect the signature XML part (/_rels/.rels signature part) and ensure each <Reference> has a non-empty Uri attribute
  2. Re-sign the package with PackageDigitalSignatureManager.Sign instead of external tools
  3. Validate the signature XML against the OPC digital signature schema before Verify
  4. Check that the signing tool writes OPC-compliant manifests (WPF/XPS compatible)

Example fix

// before (hand-crafted signature XML)
<Reference>
  <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
</Reference>
// after
<Reference Uri="/document.xaml">
  <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
  <DigestValue>...</DigestValue>
</Reference>
Defensive patterns

Strategy: validation

Validate before calling

// Pre-check the Reference XML before Verify
foreach (var sig in package.GetParts()) { /* locate Signature parts */ }
var doc = XDocument.Load(signaturePart.GetStream());
XNamespace ds = "http://www.w3.org/2000/09/xmldsig#";
bool allHaveUri = doc.Descendants(ds + "Reference")
    .All(r => !string.IsNullOrEmpty((string)r.Attribute("Uri")));
if (!allHaveUri) throw new InvalidDataException("Reference missing Uri attribute");

Try / catch

try
{
    var status = sigManager.VerifySignatures(true);
}
catch (XmlException ex) when (ex.Message.Contains("Uri"))
{
    // treat package as unsigned/corrupt: quarantine and re-sign
}

Prevention

When it happens

Trigger: Calling PackageDigitalSignatureManager.Verify (or opening a signed package) where a <Reference> element in the Signature part lacks the Uri attribute, or has an empty/malformed Uri value that fails part-URI parsing.

Common situations: Signature files hand-edited or regenerated by third-party signing tools that do not emit the Uri attribute; truncated/corrupted signature XML after partial file transfer; non-OPC signing tools writing plain XMLDSig without OPC's required attributes.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7c5b56d216f803f3. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/IO/Packaging/XmlSignatureManifest.cs:220

        private static Uri ParsePartUri(XmlReader reader, out ContentType contentType)
        {
            // should be a relative Package uri with a query portion that contains the ContentType
            contentType = ContentType.Empty;
            Uri partUri = null;

            // must be one and only one attribute
            if (PackagingUtilities.GetNonXmlnsAttributeCount(reader) == 1)
            {
                string uriAttrValue = reader.GetAttribute(XTable.Get(XTable.ID.UriAttrName));
                if (uriAttrValue != null)
                {
                    partUri = ParsePartUriAttribute(uriAttrValue, out contentType);
                }
            }

            // will be null if we had no success
            if (partUri == null)
                throw new XmlException(SR.Format(SR.RequiredXmlAttributeMissing, XTable.Get(XTable.ID.UriAttrName)));

            return partUri;
        }

        /// <summary>
        /// Parses a Reference tag
        /// </summary>
        /// <param name="reader"></param>
        /// <returns>partManifestEntry that represents the state of the tag</returns>
        private static PartManifestEntry ParseReference(XmlReader reader)
        {
            Debug.Assert(reader != null);

            // <Reference> found - get part Uri from the tag
            ContentType contentType = null;
            Uri partUri = ParsePartUri(reader, out contentType);

            // only allocate if this turns out to be a Relationship transform

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