diff --git a/protocol/authenticator.go b/protocol/authenticator.go
index dbdbcf5..c889c80 100644
--- a/protocol/authenticator.go
+++ b/protocol/authenticator.go
@@ -7,7 +7,10 @@ import (
 	"github.com/duo-labs/webauthn/protocol/webauthncbor"
 )
 
-var minAuthDataLength = 37
+var (
+	minAuthDataLength     = 37
+	minAttestedAuthLength = 55
+)
 
 // Authenticators respond to Relying Party requests by returning an object derived from the
 // AuthenticatorResponse interface. See §5.2. Authenticator Responses
@@ -158,8 +161,11 @@ func (a *AuthenticatorData) Unmarshal(rawAuthData []byte) error {
 	remaining := len(rawAuthData) - minAuthDataLength
 
 	if a.Flags.HasAttestedCredentialData() {
-		if len(rawAuthData) > minAuthDataLength {
-			a.unmarshalAttestedData(rawAuthData)
+		if len(rawAuthData) > minAttestedAuthLength {
+			validError := a.unmarshalAttestedData(rawAuthData)
+			if validError != nil {
+				return validError
+			}
 			attDataLen := len(a.AttData.AAGUID) + 2 + len(a.AttData.CredentialID) + len(a.AttData.CredentialPublicKey)
 			remaining = remaining - attDataLen
 		} else {
@@ -188,11 +194,15 @@ func (a *AuthenticatorData) Unmarshal(rawAuthData []byte) error {
 }
 
 // If Attestation Data is present, unmarshall that into the appropriate public key structure
-func (a *AuthenticatorData) unmarshalAttestedData(rawAuthData []byte) {
+func (a *AuthenticatorData) unmarshalAttestedData(rawAuthData []byte) error {
 	a.AttData.AAGUID = rawAuthData[37:53]
 	idLength := binary.BigEndian.Uint16(rawAuthData[53:55])
+	if len(rawAuthData) < int(55+idLength) {
+		return ErrBadRequest.WithDetails("Authenticator attestation data length too short")
+	}
 	a.AttData.CredentialID = rawAuthData[55 : 55+idLength]
 	a.AttData.CredentialPublicKey = unmarshalCredentialPublicKey(rawAuthData[55+idLength:])
+	return nil
 }
 
 // Unmarshall the credential's Public Key into CBOR encoding
diff --git a/protocol/authenticator_test.go b/protocol/authenticator_test.go
index bc42b04..941ef52 100644
--- a/protocol/authenticator_test.go
+++ b/protocol/authenticator_test.go
@@ -184,9 +184,10 @@ func TestAuthenticatorData_unmarshalAttestedData(t *testing.T) {
 		rawAuthData []byte
 	}
 	tests := []struct {
-		name   string
-		fields fields
-		args   args
+		name    string
+		fields  fields
+		args    args
+		wantErr bool
 	}{
 		// TODO: Add test cases.
 	}
@@ -199,7 +200,9 @@ func TestAuthenticatorData_unmarshalAttestedData(t *testing.T) {
 				AttData:  tt.fields.AttData,
 				ExtData:  tt.fields.ExtData,
 			}
-			a.unmarshalAttestedData(tt.args.rawAuthData)
+			if err := a.unmarshalAttestedData(tt.args.rawAuthData); (err != nil) != tt.wantErr {
+				t.Errorf("AuthenticatorData.unmarshalAttestedData() error = %v, wantErr %v", err, tt.wantErr)
+			}
 		})
 	}
 }