diff --git a/lemur/certificates/service.py b/lemur/certificates/service.py
index b05f489a0..1c47880f5 100644
--- a/lemur/certificates/service.py
+++ b/lemur/certificates/service.py
@@ -1046,9 +1046,31 @@ def is_attached_to_endpoint(certificate_name, endpoint_name):
     This method talks to elb and finds the real time information.
     :param certificate_name:
     :param endpoint_name:
-    :return: True if certificate is attached to the given endpoint, False otherwise
+    :return: True if certificate is attached to the given endpoint, False otherwise.
+        Returns False when the endpoint no longer exists (nothing to be attached to).
+        When the source plugin cannot verify attachment (does not implement
+        get_endpoint_certificate_names()), returns True (fail-closed) so a possibly
+        still-deployed certificate is never silently revoked.
     """
     endpoint = endpoint_service.get_by_name(endpoint_name)
+    if endpoint is None:
+        current_app.logger.error(
+            "Endpoint %s not found; assuming certificate %s is not attached",
+            endpoint_name,
+            certificate_name,
+        )
+        capture_exception()
+        return False
+    if not hasattr(endpoint.source.plugin, "get_endpoint_certificate_names"):
+        current_app.logger.error(
+            "Source plugin %s does not implement 'get_endpoint_certificate_names()'; "
+            "assuming certificate %s is attached to endpoint %s (fail-closed)",
+            endpoint.source.plugin_name,
+            certificate_name,
+            endpoint_name,
+        )
+        capture_exception()
+        return True
     attached_certificates = endpoint.source.plugin.get_endpoint_certificate_names(
         endpoint
     )
diff --git a/lemur/tests/test_certificates.py b/lemur/tests/test_certificates.py
index 53be9a845..50a5e4f34 100644
--- a/lemur/tests/test_certificates.py
+++ b/lemur/tests/test_certificates.py
@@ -2037,3 +2037,74 @@ def test_send_source_destination_pairing_metrics(certificate):
     assert dst_tags_by_name["shared"]["datacenter"] == "us1.prod"
     assert dst_tags_by_name["orphan-dst"]["has_source"] == "false"
     assert "datacenter" not in dst_tags_by_name["orphan-dst"]
+# is_attached_to_endpoint — hasattr guard tests
+# ---------------------------------------------------------------------------
+
+
+def test_is_attached_to_endpoint_plugin_missing_method(app):
+    """Plugin without get_endpoint_certificate_names returns True (fail-closed, no AttributeError)."""
+    from unittest.mock import MagicMock, patch
+    from lemur.certificates.service import is_attached_to_endpoint
+
+    plugin = MagicMock(spec=[])  # spec=[] → hasattr returns False for everything
+    plugin.plugin_name = "test-no-method-source"
+    source = MagicMock()
+    source.plugin = plugin
+    endpoint = MagicMock()
+    endpoint.source = source
+
+    with patch("lemur.certificates.service.endpoint_service") as mock_ep_svc:
+        mock_ep_svc.get_by_name.return_value = endpoint
+        result = is_attached_to_endpoint("my-cert", "my-endpoint")
+
+    assert result is True
+
+
+def test_is_attached_to_endpoint_endpoint_not_found(app):
+    """Endpoint lookup returning None returns False (no AttributeError) — nothing to be attached to."""
+    from unittest.mock import patch
+    from lemur.certificates.service import is_attached_to_endpoint
+
+    with patch("lemur.certificates.service.endpoint_service") as mock_ep_svc:
+        mock_ep_svc.get_by_name.return_value = None
+        result = is_attached_to_endpoint("my-cert", "missing-endpoint")
+
+    assert result is False
+
+
+def test_is_attached_to_endpoint_plugin_has_method_cert_present():
+    """Plugin with get_endpoint_certificate_names returns True when cert is in list."""
+    from unittest.mock import MagicMock, patch
+    from lemur.certificates.service import is_attached_to_endpoint
+
+    plugin = MagicMock()
+    plugin.get_endpoint_certificate_names.return_value = ["my-cert", "other-cert"]
+    source = MagicMock()
+    source.plugin = plugin
+    endpoint = MagicMock()
+    endpoint.source = source
+
+    with patch("lemur.certificates.service.endpoint_service") as mock_ep_svc:
+        mock_ep_svc.get_by_name.return_value = endpoint
+        result = is_attached_to_endpoint("my-cert", "my-endpoint")
+
+    assert result is True
+
+
+def test_is_attached_to_endpoint_plugin_has_method_cert_absent():
+    """Plugin with get_endpoint_certificate_names returns False when cert not in list."""
+    from unittest.mock import MagicMock, patch
+    from lemur.certificates.service import is_attached_to_endpoint
+
+    plugin = MagicMock()
+    plugin.get_endpoint_certificate_names.return_value = ["other-cert"]
+    source = MagicMock()
+    source.plugin = plugin
+    endpoint = MagicMock()
+    endpoint.source = source
+
+    with patch("lemur.certificates.service.endpoint_service") as mock_ep_svc:
+        mock_ep_svc.get_by_name.return_value = endpoint
+        result = is_attached_to_endpoint("my-cert", "my-endpoint")
+
+    assert result is False