diff --git a/defects/hazelcast/patch/hazelcast-0001-serializationutil-getinterfaces-diamond.md b/defects/hazelcast/patch/hazelcast-0001-serializationutil-getinterfaces-diamond.md
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+# UNDF: (pending)
+# hazelcast-0001: SerializationUtil.getInterfaces — O(2^D) diamond re-traversal; Collections.addAll() return value ignored
+
+## CWE-407 — Algorithmic Complexity: O(2^D) recursive diamond re-traversal in interface hierarchy collection for serializer lookup
+
+| Field        | Value |
+|--------------|-------|
+| ID           | hazelcast-0001 |
+| Severity     | HIGH |
+| Ecosystem    | hazelcast |
+| Package      | hazelcast |
+| File         | `hazelcast/src/main/java/com/hazelcast/internal/serialization/impl/SerializationUtil.java` |
+| Lines        | 150–158 |
+| Complexity   | O(2^D) on diamond interface hierarchies |
+| Hot path     | Called per serialization of a type not yet seen by the serialization service (first-time serializer lookup) |
+
+## Defect
+
+`SerializationUtil.getInterfaces` recursively collects all interfaces of a class into a `Set<Class<?>>`.
+Although it uses a Set, the recursion guard is MISSING — `Collections.addAll(interfaces, classes)` fills
+the set but the `for` loop then recurses into every interface unconditionally, regardless of whether
+each was already present in the set:
+
+```java
+// SerializationUtil.java:150-158 (DEFECT)
+static void getInterfaces(Class<?> clazz, Set<Class<?>> interfaces) {
+    final var classes = clazz.getInterfaces();
+    if (classes.length > 0) {
+        Collections.addAll(interfaces, classes);    // adds to set (ignored return vals)
+        for (Class<?> cl : classes) {
+            getInterfaces(cl, interfaces);           // DEFECT: recurses unconditionally
+        }                                            // ignores whether cl was already present
+    }
+}
+```
+
+On a diamond hierarchy (interface I1 extends Base; interface I2 extends Base; class C implements I1, I2):
+- `getInterfaces(C)`:
+  - `Collections.addAll(interfaces, [I1, I2])` → both added
+  - recurse into I1: `getInterfaces(I1)`:
+    - adds Base to set, recurses into Base
+  - recurse into I2: `getInterfaces(I2)`:
+    - `Collections.addAll(interfaces, [Base])` → Base already present, add() returns false (IGNORED)
+    - STILL recurses into Base → unnecessary re-traversal
+
+At diamond depth D, Base is visited 2^D times.
+
+Called from `AbstractSerializationService.lookupCustomSerializer()` (line 663, and again once per
+superclass in the superclass chain at line 669), which is invoked on every first serialization
+of a previously-unseen class type.
+
+## Fix
+
+Replace `Collections.addAll + unconditional loop` with a per-element `interfaces.add()` guard:
+
+```java
+// AFTER — O(N+E) where N=interfaces, E=inheritance edges
+static void getInterfaces(Class<?> clazz, Set<Class<?>> interfaces) {
+    for (Class<?> cl : clazz.getInterfaces()) {
+        if (interfaces.add(cl)) {           // add returns false if already present → skip
+            getInterfaces(cl, interfaces);  // only recurse if newly added
+        }
+    }
+}
+```
+
+## Speedup
+
+| Diamond depth (D) | Before (visits) | After (visits) | Speedup |
+|------------------|----------------|----------------|---------|
+| 5                | 31             | 5              | 6×      |
+| 10               | 1,023          | 10             | 102×    |
+| 15               | 32,767         | 15             | 2,184×  |
+| 20               | 1,048,575      | 20             | 52,428× |
+
+Growth before: O(2^D). Growth after: O(D).