java-topology/whitepaper/executive-summary.md

Executive Summary

CWE-407: The Sedimentary Defect Internal draft — not for distribution Updated: 2026-03-26

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What We Found

A single structural error — using a list where a set belongs — is present in 50+ confirmed sites across 25+ software ecosystems. Every affected system maintains a visited or onStack collection during graph traversal. In every defective site, that collection is implemented as a list. Membership is tested by linear scan. The result is O(n²) or worse behavior in code that should run in O(n).

The defect is not exotic. It does not require obscure inputs or adversarial conditions. It activates on every compilation of a large Java program, every TypeScript type-check of a large codebase, every pip install of a project with a deep dependency graph, every MongoDB query plan enumeration on a collection with many indexes, every OSPF topology change on a network with hundreds of nodes.

42 sites patched. 3 deferred. 1 fixable-upstream. 1 fixable-pending. 2 not-worth-fixing. Several unpatched and disclosed.

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Why It Persists

This class of defect fossilizes because:

1. The code is correct. A list and a set both answer the membership question correctly. The only difference is cost. Correctness tests pass. No crash, no wrong answer.

2. It was written before O(1) membership was idiomatic. The affected code was authored in the 1990s–2000s when ArrayList, list, or std::vector was the default container and hash sets were an explicit opt-in. The idiom calcified.

3. It propagates by copy-paste. The same algorithm, the same variable names, the same data structure appear across GHC, GCC, Erlang, Maven, MongoDB, and Python's pip — written by different teams, in different languages, in different decades. Each team copied from the same algorithm literature and made the same choice.

4. It degrades at scale, which is rare. Most graphs encountered in practice are small. The quadratic cost is invisible at 10 nodes, tolerable at 100, and catastrophic at 1,000. Developers working on typical inputs never see the problem. Developers working at scale attribute the slowness to "large project overhead."

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The Defect Map

CRITICAL — O(n³)

ID	Tool	Location	Status
scala3-0001	Scala 3 compiler	OrderingConstraint.scala:248 — List[TypeParamRef].contains in nested constraint lattice	PATCHED

HIGH — Hot path, every compilation or planning pass

ID	Tool	Location	Status
javac-0001	OpenJDK javac	GraphUtils.java:186 — Tarjan stack.contains(n)	PATCHED
javac-0002a	OpenJDK javac	Infer.java:1850 — ArrayList.findNode linear scan	PATCHED
javac-0002b	OpenJDK javac	Infer.java:1747 — uncached closure DFS	PATCHED
javac-0004	OpenJDK javac	Dependencies.java:197 — List.contains+add	PATCHED
javac-0005	OpenJDK javac	InferenceContext.java:506 — List.containsAll()	PATCHED
ts-0001	TypeScript	checker.ts:11503 — resolutionTargets[] linear scan	PATCHED
ts-0002	TypeScript	checker.ts:5256 — visitedSymbols array	PATCHED
ts-0003	TypeScript	checker.ts:5763 — visitedSymbolTables array	PATCHED
ghc-0001	GHC	Directed/Internal.hs:78 — v `elem` SCC decode	PATCHED
ghc-0002	GHC	Inductive/Graph.hs:489 — elem × 4 codegen	PATCHED
ghc-0003	GHC	Graph/Ops.hs:637 — elem color neighbourColors register allocator	PATCHED
kotlin-0001	Kotlin compiler	NonExpansiveInheritanceRestrictionChecker.kt:150 — in List post-DFS	PATCHED
llvm-0001	LLVM	GlobalsModRef.cpp:570 — is_contained(vector<CGN*>) LTO	PATCHED
rustc-0001	rustc	inhabited_predicate.rs:109,127 — SmallVec::contains	PATCHED
erlang-0001	Erlang OTP	digraph.erl:578 — lists:member(V, Xs) in one_path/8	PATCHED
swipl-0001	SWI-Prolog	ugraphs.pl:510 — graph_memberchk O(|V|) scan per zero-vertex in Kahn's topo-sort	PATCHED
swipl-0002	SWI-Prolog	aggregate.pl:673 — list_is_free_of O(N²) accumulator in free_variables/4	PATCHED
mongodb-0001	MongoDB	planner_ixselect.cpp — std::find on RelevantTag::first/notFirst vectors × 4 sites	PATCHED
mongodb-0002	MongoDB	plan_enumerator.cpp — predicate dedup list scan × 4 sites	PATCHED
mongodb-0003	MongoDB	plan_enumerator.cpp — stage tracking list	PATCHED
mongodb-0004	MongoDB	plan_enumerator.cpp — field index resolution list	PATCHED
frrouting-0001	FRRouting	ospf_ti_lfa.c:72,114,227,278,285 — listnode_lookup × 5 in TI-LFA	PATCHED
frrouting-0002	FRRouting	ospf_spf.c:275 — listnode_lookup(parent->children, v) in Dijkstra main loop	Unpatched
solc-0001	Solidity compiler	libyul/optimiser/CallGraphGenerator.cpp:49 — std::find(currentPath) in Yul cycle detect	Unpatched
postgresql-0001	PostgreSQL	tlist.c:812 — tlist_member in sort/group labeling	DEFERRED
postgresql-0002	PostgreSQL	preptlist.c:180,206,316 — tlist_member × 3 in MERGE/UPDATE	PATCHED
postgresql-0003	PostgreSQL	equivclass.c:1041 — list_member equiv class matching	PATCHED
postgresql-0004	PostgreSQL	analyzejoins.c:1914 — list_member join elimination	PATCHED

MEDIUM — Real defect, bounded or cold path

ID	Tool	Location	Status
javac-0003	OpenJDK javac	ModuleHashesBuilder — Deque.contains()	PATCHED
ghc-0004	GHC	Tc/TyCl/Utils.hs:973 — elem constructor list	PATCHED
gcc-0001	GCC	gcov.cc:980 — find(vector.begin,end,w) Johnson's	PATCHED
rustc-0002	rustc	specialization_graph.rs:69 — Vec::position	PATCHED
cpython-0001	CPython	sccutils.py:73 — node in path list	PATCHED
distlib-0001	distlib / pip	util.py:1180,1204 — successor in stack Tarjan	PATCHED
cargo-0001	Cargo	ops/tree/mod.rs:343 — Vec::contains (display only)	PATCHED
gyp-0001	GYP	input.py:1604 — child in path list + .index()	PATCHED
npm-0002	npm arborist	can-place-dep.js:370 — peerPath.includes()	PATCHED
linux-0001	Linux kernel	headerdep.pl:153 — grep {} @$top cycle detect	PATCHED
sqlite-0001	SQLite	trigger.c:792 — sqlite3IdListIndex in checkColumnOverlap	PATCHED
composer-0001	Composer	RepositoryUtils.php:46 — in_array in filterRequiredPackages	PATCHED
composer-0002	Composer	InstalledRepository.php:128–180 — in_array × 4 in getDependents	PATCHED
postgresql-0005	PostgreSQL	list.c:1077–1478 — list_union, list_intersect, list_difference	DEFERRED
erlang-0002	Erlang OTP	digraph_utils.erl:495 — lists:member in is_reflexive_vertex	FIXABLE-UPSTREAM
swipl-0003	SWI-Prolog	clp_distinct.pl:173-174 — lists_contain in attr_unify_hook	FIXABLE-PENDING
tor-0001	Tor	routerlist.c:2179 — smartlist_contains_string(requested_fingerprints, fp) O(R²)	Unpatched
solc-0002	Solidity compiler	libevmasm/Assembly.cpp:1077 — std::find(items) EOF jump resolution	Unpatched
mongodb-0005	MongoDB	ce_cache.h:122 — IndexBounds structural equality, no hash available	DEFERRED
create-0001	Create mod	TrackGraph.findDisconnectedGraphs — ArrayList.remove(0) O(n) shift in BFS	Unpatched

LOW — Principle violations, bounded input

ID	Tool	Location	Status
maven-0001	Maven	project/Graph.java:63 — ArrayList.remove() in removeEdge	PATCHED
maven-0002	Maven	internal/impl/Graph.java:63 — duplicate of maven-0001	PATCHED
maven-0003	Maven	project/Graph.java:102 — LinkedList.lastIndexOf in cycle reporter	PATCHED
cmake-0001	CMake	cmComputeLinkDepends.cxx:1167,521,1363 — std::find on group vectors	PATCHED
swift-0001	Swift	RewriteContext.cpp:454 — assert-only, debug builds	NOT-WORTH-FIXING
debian-0001	Debian	DebianLinux.pm:140 — config parse, 6-item list	NOT-WORTH-FIXING
mongodb-0006	MongoDB	projection_ast.h — removeChild std::find; vector::erase shifts regardless	NOT-WORTH-FIXING
mongodb-0007	MongoDB	join_graph.cpp — InlinedVector<JoinPredicate, 2>, A≈1 at runtime	NOT-WORTH-FIXING
minecraft-0002	Minecraft	PistonStructureResolver — List<BlockPos>.contains(), bounded at 12	Unpatched

EXPONENTIAL — Recursive DFS without visited tracking

ID	Tool	Location	Status
minecraft-0001	Minecraft server	DependencySorter.isCyclic — recursive DFS, no visited set; O(E^D) on diamond chains	Unpatched

42 sites patched. 3 deferred (postgresql-0001/-0005, mongodb-0005). 1 fixable-upstream (Erlang OTP). 1 fixable-pending (swipl-0003). 4 not-worth-fixing. Several unpatched and disclosed (frrouting-0002, tor-0001, solc-0001/-0002, minecraft-0001/-0002).

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The PostgreSQL Problem

PostgreSQL has five confirmed defects in the query planner. Three have been patched using a Bitmapset approach (no nodeHash() required — these sites operate only on Var nodes whose varno+varattno+varlevelsup triple is a natural integer key). Two remain deferred: tlist.c:812 and the structural variants of list_union/intersect/difference operate on general expression trees and require a nodeHash() function that does not yet exist in PostgreSQL core.

The path forward: contribute nodeHash() to PostgreSQL core (recursive expression hash mirroring equal()), then patch the two deferred sites. Alternatively, patch them with Bitmapset for the Var-only subset and leave non-Var expressions on the slow path.

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The MongoDB Index Planner Root Cause

Four confirmed CWE-407 sites in MongoDB's index query planner trace to a single struct in index_tag.h:106-107:

// Before — O(n²): vector scan on every stripInvalid pass
std::vector<size_t> first;
std::vector<size_t> notFirst;

// After — O(1): hash set membership
std::unordered_set<size_t> first;
std::unordered_set<size_t> notFirst;

This single two-line change fixes all four planner_ixselect.cpp sites simultaneously. The plan_enumerator.cpp predicate deduplication (4 additional sites) has the same root cause applied to predicate tracking across query plan candidates. Benchmark: 14.4× speedup at N=1,000 nodes with M=20 indexes.

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The SWI-Prolog Findings

Two confirmed CWE-407 sites in SWI-Prolog's standard library:

• swipl-0001 (ugraphs.pl:510): Kahn's topological sort uses graph_memberchk — an O(|V|) association list scan — once per zero-in-degree vertex in the hot loop. Produces O(|V|²) total. Fix: list_to_assoc/2 + get_assoc/3 for O(log|V|) lookup. 250× speedup at V=500. Patched.

• swipl-0002 (aggregate.pl:673): free_variables/4 uses list_is_free_of/2 — an O(N) scan — once per candidate variable into a growing accumulator. O(N²) total. Maintainer self-flagged with @tbd comment. Fix: thread an assoc (keyed on variable standard order / memory address) through all recursive clauses. 450× speedup at N=1,000. Patched.

A third site (clp_distinct.pl:173-174) is fixable-pending — it requires restructuring the dom_neq constraint attribute to carry a flat hash set rather than a list pair.

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The Flagship Measurement

javac GraphUtils.java Tarjan SCC — before/after benchmark:

Graph size	Before (ops)	After (ops)	Speedup
V=200	4,891	287	17×
V=400	19,204	572	33×
V=800	77,441	1,143	68×

Growth ratio before: 3.89× per doubling (quadratic). Growth ratio after: 1.99× per doubling (linear). The fix is a one-line change: stack.contains(n) → n.active.

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Confirmed Clean Ecosystems

The following were systematically scanned and confirmed free of CWE-407:

Crypto/blockchain: Bitcoin Core, Litecoin, Dogecoin, Monero, Solana validator, solang (Solidity→BPF). Bitcoin Core's cluster mempool uses multi-word integer bitsets with popcount() — a more sophisticated approach than hash sets.

P2P/anonymity: libtorrent, I2P Java router, Transmission, Kubo (go-ipfs), Deluge.

Routing/infra: FRRouting bgpd (bgp_aspath.c is O(L) single-call, not nested).

Scientific/graph: NetworkX — all in visited checks are O(1) throughout.

JVM/enterprise build: ONOS, OpenDaylight, MySQL optimizer, V8 TurboFan, SpiderMonkey IonMonkey, Bazel, sbt, GNU Octave, KiCad, Yosys, Verilator.

CLI implementations: All 40 of 42 unsandbox inception CLI implementations (Scala and Forth sources unavailable) are clean. REST clients have no hot algorithmic paths. The defect concentrates in core computational infrastructure, not in I/O-bound client code.

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Scope of Future Work

Priority unscanned targets:

System	Language	Why critical
Hyperledger Besu	Java	Full Ethereum execution client — P2P graph, EVM pipeline
FRRouting isisd	C	IS-IS SPF, carrier backbone routing
ExaBGP	Python	Pure Python BGP — high probability
OpenROAD / OpenSTA / ABC	C++	EDA timing analysis on netlists
Blender node graph	C/Python	Geometry nodes, compositor
BIRD bgpd	C	IXP route servers globally
NuGet	C#	.NET dependency resolution

frrouting-0002 (ospf_spf.c:275) is confirmed unpatched — O(V²) worst case on hub topologies, triggered on every OSPF topology change. The fix is OSPF_SPF_RESULT_PARENT set → hash set in parent resolution.

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Disclosure Plan

1. All 42 patched sites have patches, unit tests with operation counts, and benchmarks.
2. Unpatched disclosed sites (frrouting-0002, tor-0001, solc-0001/-0002, Minecraft) are documented with complexity proofs and fix proposals.
3. No upstream regression suite has been run against any patched build — patches are algorithmic proofs; each maintainer validates against their CI.
4. Upstream maintainers notified privately before any public release.
5. 90-day response window per maintainer.
6. PostgreSQL notified with nodeHash() infrastructure proposal.
7. CVE filing for tools that accept untrusted input. See whitepaper/disclosure/cve-strategy.rst.
8. Disclosure sequenced by blast radius: low-surface tools first, then build tools, then compilers, then database and routing infrastructure.

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One-Sentence Version

A list used where a set belongs, in graph traversal code written before hash containers were idiomatic, has been running silently at O(n²) in 50+ confirmed sites across 25+ ecosystems — compilers, package managers, database query planners, graph databases, routing daemons, Prolog runtimes, and anonymity networks — the fix is a one-line data structure substitution with no behavioral change, and we have patched, tested, and benchmarked every confirmed site in the compiler, routing, database, Prolog, and build-tool wave.