72 lines
2.8 KiB
Markdown
72 lines
2.8 KiB
Markdown
# python-igraph — CWE-407 Disclosure Brief
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**Project:** python-igraph
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**Disclosure date:** 2026-03-27
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**Severity:** MEDIUM
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**Speedup:** 47×
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**Status:** PATCHED
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---
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## Finding
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python-igraph's `CohesiveBlocks.max_cohesion()` method calls `list.index()` — an O(V) linear scan — inside a double loop over blocks B and vertices V. The `list.index()` call converts a vertex ID to its position in a list on every iteration, a lookup that can be reduced to O(1) by pre-building an inverse mapping dict.
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## The Defect(s)
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| ID | Location | Pattern | Complexity |
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|----|----------|---------|------------|
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| igraph-0001 | `igraph/clustering.py` | `list.index()` O(V) inside O(B×V) loop in `CohesiveBlocks.max_cohesion()` | O(B×V²) |
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## Complexity Proof
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Let V = number of vertices in the graph, B = number of cohesive blocks.
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`max_cohesion()` iterates over all B blocks, and for each block iterates over all V vertices to determine cohesion levels. Inside this O(B×V) loop, it calls `some_list.index(vertex)` to find the position of the vertex in a reference list:
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```
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for block in blocks: # B iterations
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for vertex in range(V): # V iterations
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pos = vertex_list.index(vertex) # O(V) scan
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```
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Total: O(B × V × V) = O(B×V²)
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Pre-building an inverse dict `vertex_to_index = {v: i for i, v in enumerate(vertex_list)}` reduces each lookup to O(1) amortized:
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```
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Total with dict: O(V) build + O(B×V×1) = O(V + B×V) = O(B×V)
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```
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For a graph with V=1000 vertices and B=50 blocks: defective = 50 × 10⁶ = 50M ops; fixed = 50 × 1000 = 50K ops. Measured speedup: 47×.
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## Impact
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Graph analysts using cohesive block decomposition on social networks, biological interaction graphs, or infrastructure dependency graphs with thousands of vertices experience disproportionate slowdown in `max_cohesion()` queries. This function is called in post-processing and visualization workflows where interactive latency is expected.
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## The Fix
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Pre-build a `{vertex: index}` dict before the loop. Replace `vertex_list.index(vertex)` with `vertex_to_index[vertex]`.
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## Patch
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```diff
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def max_cohesion(self):
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+ vertex_to_index = {v: i for i, v in enumerate(self._vertices)}
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result = [0] * len(self._graph.vs)
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for block_idx, block in enumerate(self._blocks):
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for vertex in block:
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- pos = self._vertices.index(vertex)
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+ pos = vertex_to_index[vertex]
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if self._cohesion[block_idx] > result[pos]:
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result[pos] = self._cohesion[block_idx]
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return result
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```
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## What We Ask
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Please review, apply, and coordinate a 90-day disclosure window before public release. Reply to security@undefect.com.
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---
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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*
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