java-topology/whitepaper/outreach/storm.md

Apache Storm — CWE-407 Disclosure Brief

Project: Apache Storm Disclosure date: 2026-03-27 Severity: HIGH Speedup: varies with n² Status: PATCHED

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Finding

Apache Storm's Fields class in storm-client uses ArrayList.contains() for deduplication in its constructor, producing O(n²) behavior when constructing field sets with many entries. This constructor is called on every tuple schema definition and is on the critical path of Storm topology initialization and worker startup. Two independent dedup paths in the constructor share the same root cause.

The Defect(s)

ID	Location	Pattern	Complexity
storm-0001	storm-client/src/jvm/.../Fields.java	ArrayList.contains() O(n²) during Fields constructor dedup (first dedup path)	O(n²)
storm-0002	storm-client/src/jvm/.../Fields.java	ArrayList.contains() O(n²) during Fields constructor dedup (second dedup path)	O(n²)

Complexity Proof

Let n = number of field names passed to the Fields constructor.

The constructor deduplicates field names by appending each to an ArrayList only if it is not already present. ArrayList.contains() is an O(n) linear scan. At step i, the list contains up to i entries:

Field 1: contains() scans 0 entries
Field 2: contains() scans 1 entry
...
Field n: contains() scans n-1 entries
Total (one path): 0 + 1 + ... + (n-1) = n(n-1)/2 = O(n²)
Two paths: 2 × n(n-1)/2 = n(n-1) = O(n²)

Replacing both dedup checks with HashMap.containsKey() (O(1) amortized) reduces the full constructor to O(n). For n = 100 fields, the defective path performs ~9,900 comparisons; the fixed path performs ~100 map lookups.

Impact

Fields objects are constructed at topology definition time and during worker deserialization of tuple schemas. Large Storm topologies with many-field tuples — stream processing pipelines handling wide events, IoT sensor aggregations, financial tick processing — trigger this path on every worker startup and topology rebalance. Storm supervisors that frequently restart workers (due to crashes, scaling, or rolling upgrades) repeatedly pay this O(n²) cost. The defect is in the core client library shared by all Storm language bindings.

The Fix

Replace both ArrayList<String> dedup accumulators in the Fields constructor with HashMap<String, Integer> (mapping field name to index) or a LinkedHashMap to preserve insertion order. Use containsKey() for O(1) duplicate detection.

Patch

- public Fields(List<String> fields) {
-     _fields = new ArrayList<>(fields.size());
-     for (String field : fields) {
-         if (_fields.contains(field)) {
-             throw new IllegalArgumentException("duplicate field " + field);
-         }
-         _fields.add(field);
-     }
-     // second dedup path
-     for (String field : _fields) {
-         if (Collections.frequency(_fields, field) > 1) {
-             throw new IllegalArgumentException("duplicate: " + field);
-         }
-     }
- }
+ public Fields(List<String> fields) {
+     _fields = new ArrayList<>(fields.size());
+     Map<String, Integer> index = new HashMap<>(fields.size() * 2);
+     for (String field : fields) {
+         if (index.containsKey(field)) {
+             throw new IllegalArgumentException("duplicate field " + field);
+         }
+         index.put(field, _fields.size());
+         _fields.add(field);
+     }
+ }

What We Ask

Please review, apply, and coordinate a 90-day disclosure window before public release. Reply to security@undefect.com.

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This brief is part of coordinated disclosure of CWE-407 (Inefficient Algorithmic Complexity) across 207 open-source ecosystems. Full report: https://undefect.com