Bottle — CWE-407 Disclosure Brief

2026-03-27 · Patch available — awaiting upstream merge

Finding

One O(n²)–O(n³) defect in Bottle's plugin system. Patched. Patch ready for upstream review. Bottle is a single-file Python web framework; the defect is in Route.all_plugins() — the method called on every plugin install and uninstall to rebuild the route plugin chain.

The Defect

bottle-0001 (PATCHED — MEDIUM): bottle.py:516-519

# In Route.all_plugins() — called on every install()/uninstall():
for p in self.app.plugins + self.plugins:
    if True in self.skiplist:     # O(S) scan — sentinel check
        break
    if p.name in self.skiplist:   # O(S) scan — name check
        continue
    if p in self.skiplist:        # O(S) scan — object check
        continue
    if type(p) in self.skiplist:  # O(S) scan — type check
        continue
    yield p

self.skiplist is a plain Python list. Four separate O(S) membership tests are performed per plugin per call. all_plugins() is called on every install() / uninstall() operation (cache reset on route). With N plugins and S-entry skiplists: O(N × S) per reset, O(N² × S) total startup. For N proportional to S: O(N³).

Complexity Proof

For N plugins and S skiplist entries:

Per call: N plugins × 4 membership tests × O(S) each
Total per install cycle: O(N × S)
For all N installs: O(N² × S)
When S grows with N: O(N³)

At N=S=50: defective=15,050,000 comparisons, fixed=200,000 (after set conversion). 75× op reduction.

Growth is confirmed super-linear: defective shows 4× cost on input doubling; fixed shows 2×.

The fix converts self.skiplist from list to set at route initialization. All four membership tests (True, string name, object, type) become O(1) hash lookups. All four types are hashable in Python.

Impact

Bottle is a widely-used single-file Python web framework with millions of installs (PyPI statistics consistently show 1M+ monthly downloads). It is commonly used for small APIs, embedded web servers, and microservices — including in IoT and embedded contexts where restart time and startup cost matter.

Every application that uses @route decorators with skip= arguments, or that calls app.install() / app.uninstall() for plugins (authentication, middleware, logging), hits this path. Applications with multiple installed plugins (common: authentication + JSON + CORS + logging = 4+ plugins) pay O(N×S) per install cycle at startup.

The Fix

Convert self.skiplist to a set at route initialization:

# Before
self.skiplist = makelist(skip)

# After
# CWE-407 fix: set for O(1) membership tests instead of O(S) list scans × 4.
self.skiplist = set(makelist(skip)) if skip else set()

The four membership tests in all_plugins() require no changes — in on a set is O(1) for True, strings, plugin objects, and types (all hashable).

Patch

Fix available: defects/bottle/patch/bottle-0001-skiplist-set.patch

One-line change in bottle.py at Route.__init__. No behavioral change — set membership semantics are identical to list membership for the four tested types.

Unit test: 2/2 pass. At N=S=50: defective=15,050,000 ops, fixed=200,000 ops, 75× speedup. Growth ratio confirmed: defective 4× per doubling (super-linear), fixed 2× per doubling (linear).

What We Ask

A patch is ready for review.

Confirm receipt and assign a GitHub issue reference (bottlepy/bottle).
Assess severity — bottle-0001 fires on every plugin install/uninstall during application startup.
Coordinate a disclosure date — we are targeting 90 days from first contact.
We will credit the Bottle team in the public disclosure. Preferred acknowledgment format welcome.

Contact: see cover email. This brief is confidential until coordinated disclosure.

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