diff --git a/nettacker/core/utils/common.py b/nettacker/core/utils/common.py
index 5e616ae0a..c5384b41d 100644
--- a/nettacker/core/utils/common.py
+++ b/nettacker/core/utils/common.py
@@ -31,7 +31,19 @@ def replace_dependent_response(log, response_dependent):
         return log
 
 
-def merge_logs_to_list(result, log_list=[]):
+def merge_logs_to_list(result, log_list=None):
+    """Recursively extract all 'log' values from a nested dict into a flat deduplicated list.
+
+    Args:
+        result: A dict (possibly nested) containing 'log' keys to extract.
+        log_list: Accumulator list for recursive calls. Defaults to a new empty list
+            on each top-level call to avoid mutable default argument pitfalls.
+
+    Returns:
+        A deduplicated list of extracted log values.
+    """
+    if log_list is None:
+        log_list = []
     if isinstance(result, dict):
         if "json_event" in list(result.keys()):
             if not isinstance(result["json_event"], dict):
diff --git a/tests/core/utils/test_common.py b/tests/core/utils/test_common.py
index 5e4ced398..1185094b3 100644
--- a/tests/core/utils/test_common.py
+++ b/tests/core/utils/test_common.py
@@ -96,6 +96,43 @@ def test_select_maximum_cpu_core(cpu_count_mock):
         assert common_utils.select_maximum_cpu_core("invalid") == 1
 
 
+def test_merge_logs_to_list_simple():
+    result = {"log": "error occurred"}
+    assert common_utils.merge_logs_to_list(result) == ["error occurred"]
+
+
+def test_merge_logs_to_list_nested():
+    result = {
+        "log": "outer",
+        "nested": {"log": "inner"},
+    }
+    logs = common_utils.merge_logs_to_list(result)
+    assert sorted(logs) == ["inner", "outer"]
+
+
+def test_merge_logs_to_list_no_log_key():
+    result = {"status": "ok", "data": {"value": 42}}
+    assert common_utils.merge_logs_to_list(result) == []
+
+
+def test_merge_logs_to_list_deduplicates():
+    result = {
+        "log": "same",
+        "nested": {"log": "same"},
+    }
+    assert common_utils.merge_logs_to_list(result) == ["same"]
+
+
+def test_merge_logs_to_list_no_shared_state_between_calls():
+    """Verify that consecutive calls without explicit log_list don't leak state."""
+    result_a = {"log": "first"}
+    result_b = {"log": "second"}
+    logs_a = common_utils.merge_logs_to_list(result_a)
+    logs_b = common_utils.merge_logs_to_list(result_b)
+    assert logs_a == ["first"]
+    assert logs_b == ["second"]
+
+
 def test_wait_for_threads_to_finish_all_dead():
     """All threads already finished -- should return True immediately."""
     t = MagicMock(spec=threading.Thread)