Fall back to any trust root if both x5u and x5c are missing

webauthn-server-attestation/src/integrationTest/scala/com/yubico/fido/metadata/FidoMetadataDownloaderIntegrationTest.scala

@@ -12,7 +12,6 @@ import org.scalatest.tags.Network
 import org.scalatest.tags.Slow
 import org.scalatestplus.junit.JUnitRunner
 
-import java.util.Collections
 import scala.jdk.CollectionConverters.ListHasAsScala
 
 @Slow
@@ -52,14 +51,12 @@ class FidoMetadataDownloaderIntegrationTest
         .cacheSynchronized(
           downloader
             .fetchHeaderCertChain(
-              Collections.singleton(
-                FidoMetadataDownloader.importTrustAnchor(trustRootCert)
-              ),
               downloader
                 .parseBlob(TestCaches.blobCache.get.getBytes)
                 .getBlob
-                .getHeader,
+                .getHeader
             )
+            .get
         )
         .asScala :+ trustRootCert
       for { cert <- certChain } {

webauthn-server-attestation/src/main/java/com/yubico/fido/metadata/FidoMetadataDownloader.java

@@ -1351,7 +1351,42 @@
           InvalidAlgorithmParameterException,
           FidoMetadataDownloaderException {
     final MetadataBLOBHeader header = parseResult.blob.getHeader();
-    final List<X509Certificate> certChain = fetchHeaderCertChain(trustAnchors, header);
+    final Optional<List<X509Certificate>> certChain = fetchHeaderCertChain(header);
+    if (certChain.isPresent()) {
+      return tryVerifyBlob(parseResult, trustAnchors, certChain.get());
+    } else {
+      log.debug(
+          "x5u and x5c both missing from BLOB header. Falling back to using trust anchors as BLOB signer.");
+      for (TrustAnchor ta : trustAnchors) {
+        final X509Certificate cert = ta.getTrustedCert();
+        if (cert != null) {
+          try {
+            return tryVerifyBlob(parseResult, trustAnchors, Collections.singletonList(cert));
+          } catch (FidoMetadataDownloaderException e) {
+            if (e.getReason() == Reason.BAD_SIGNATURE) {
+              log.debug("Failed to verify BLOB with trust anchor: {}", ta);
+            } else {
+              throw e;
+            }
+          } catch (SignatureException | CertPathValidatorException e) {
+            log.debug("Failed to verify BLOB with trust anchor: {}", ta);
+          }
+        }
+      }
+      throw new IllegalArgumentException("Failed to verify BLOB with any trust anchor.");
+    }
+  }
+
+  private MetadataBLOB tryVerifyBlob(
+      ParseResult parseResult, Set<TrustAnchor> trustAnchors, List<X509Certificate> certChain)
+      throws CertificateException,
+          NoSuchAlgorithmException,
+          InvalidKeyException,
+          SignatureException,
+          CertPathValidatorException,
+          InvalidAlgorithmParameterException,
+          FidoMetadataDownloaderException {
+    final MetadataBLOBHeader header = parseResult.blob.getHeader();
     final X509Certificate leafCert = certChain.get(0);
 
     final Signature signature;
@@ -1470,8 +1505,7 @@
   }
 
   /** Parse the header cert chain and download any certificates as necessary. */
-  List<X509Certificate> fetchHeaderCertChain(
-      Set<TrustAnchor> trustAnchors, MetadataBLOBHeader header)
+  Optional<List<X509Certificate>> fetchHeaderCertChain(MetadataBLOBHeader header)
       throws IOException, CertificateException {
     if (header.getX5u().isPresent()) {
       final URL x5u = header.getX5u().get();
@@ -1492,18 +1526,11 @@
         X509Certificate x509Certificate = CertificateParser.parsePem(pem);
         certs.add(x509Certificate);
       }
-      return certs;
+      return Optional.of(certs);
     } else if (header.getX5c().isPresent()) {
-      return header.getX5c().get();
+      return Optional.of(header.getX5c().get());
     } else {
-      return trustAnchors.stream()
-          .map(TrustAnchor::getTrustedCert)
-          .findFirst()
-          .map(Collections::singletonList)
-          .orElseThrow(
-              () ->
-                  new IllegalArgumentException(
-                      "x5u and x5c both missing from BLOB header, and no given trust anchor could be interpreted as an X509Certificate."));
+      return Optional.empty();
     }
   }
 
@@ -1608,7 +1635,7 @@
 
   @Value
   @Builder
   @Jacksonized
   static class TrustRootsCacheValue {
     List<String> urls;
     List<byte[]> certsDer;

webauthn-server-attestation/src/test/scala/com/yubico/fido/metadata/FidoMetadataDownloaderSpec.scala

@@ -5,6 +5,7 @@ import com.fasterxml.jackson.databind.node.ObjectNode
 import com.yubico.fido.metadata.FidoMetadataDownloader.CachePolicyDecision
 import com.yubico.fido.metadata.FidoMetadataDownloader.FidoMetadataDownloaderBuilder
 import com.yubico.fido.metadata.FidoMetadataDownloader.TrustRootsCacheValue
+import com.yubico.fido.metadata.FidoMetadataDownloader.importTrustAnchor
 import com.yubico.fido.metadata.FidoMetadataDownloaderException.Reason
 import com.yubico.internal.util.BinaryUtil
 import com.yubico.internal.util.JacksonCodecs
@@ -1958,7 +1959,13 @@ class FidoMetadataDownloaderSpec
         }
 
         it("Missing x5c means the trust root cert is used as the signer.") {
-          val (trustRootCert, caKeypair, caName) = makeTrustRootCert()
+          val (trustRootCert, caKeypair, caName) =
+            makeTrustRootCert(distinguishedName =
+              "CN=Yubico java-webauthn-server unit tests CA 1, O=Yubico"
+            )
+          val (trustRootCert0, _, _) = makeTrustRootCert(distinguishedName =
+            "CN=Yubico java-webauthn-server unit tests CA 0, O=Yubico"
+          )
           val blobJwt =
             makeBlob(
               caKeypair,
@@ -1987,7 +1994,9 @@ class FidoMetadataDownloaderSpec
               .expectLegalHeader(
                 "Kom ihåg att du aldrig får snyta dig i mattan!"
               )
-              .useTrustRoot(trustRootCert)
+              .useTrustRoots(
+                Set(trustRootCert0, trustRootCert).map(importTrustAnchor).asJava
+              )
               .useBlob(blobJwt)
               .useCrls(crls.asJava)
               .clock(Clock.fixed(CertValidFrom, ZoneOffset.UTC))