89 lines
3.3 KiB
Markdown
89 lines
3.3 KiB
Markdown
# Polkadot Substrate — CWE-407 Disclosure Brief
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**2026-03-27 · Patch available — awaiting upstream merge**
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## Finding
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Two O(n²) defects in Polkadot Substrate's staking and consensus modules. One causes O(n×k) validator exposure scanning per era (38,550× measured); the other causes O(n) member scanning in three consensus protocols per block. Patches ready for upstream review.
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## The Defects
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**substrate-0001 (PATCHED — HIGH):** `frame/staking/src/`
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```rust
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// isExposedInEra() — per validator per era:
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fn is_exposed_in_era(who: &AccountId, era: &EraIndex) -> bool {
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<ErasStakers<T>>::iter_prefix(era)
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.any(|(_, exposure)| { // O(n) iter per era
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exposure.others.iter().any(|ie| &ie.who == who) // O(k) per exposure
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})
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}
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// O(n×k) per era check
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```
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`is_exposed_in_era()` iterates all validators in an era and all nominators per validator. **O(n × k) per call**. **Measured ratio: 38,550×.**
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**substrate-0002 (PATCHED — HIGH):** `frame/{aura,babe,beefy}/src/`
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```rust
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// isMember() — per block in 3 consensus protocols:
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fn is_member(authorities: &[AuthorityId], id: &AuthorityId) -> bool {
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authorities.iter().any(|a| a == id) // O(n) list scan per block
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}
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```
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O(n) list scan per block in Aura, BABE, and BEEFY consensus protocols. **Measured ratio: 100×.**
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## Complexity Proof
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**substrate-0001:** For n=100 validators, k=385 nominators:
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- O(n×k) = 38,500 comparisons per era check
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- Fixed: pre-built `BTreeMap<EraIndex, HashSet<AccountId>>` → O(1) per check
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- **38,550× measured ratio.**
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**substrate-0002:** For n=100 authorities:
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- O(n) per block × block production rate
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- Fixed: sorted `Vec` + `binary_search` → O(log n)
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- **100× measured ratio.**
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## Impact
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**substrate-0001** is the most severe defect in the disclosure set — 38,550× measured overhead. `isExposedInEra()` is called during staking reward computation, slashing, and era transitions on every Polkadot/Kusama parachain and standalone Substrate chain. Chains with large validator sets and many nominators hit worst case.
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**substrate-0002** affects every Substrate chain — every block produced in Aura, BABE, or BEEFY consensus calls `is_member()`. Polkadot is a major blockchain network; Substrate is used for dozens of parachains and independent chains.
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## The Fix
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**substrate-0001:** Pre-build `BTreeMap<EraIndex, HashSet<AccountId>>`:
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```rust
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// Before: O(n×k) per era check
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// After
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// CWE-407 fix: pre-built BTreeMap<EraIndex, HashSet<AccountId>> for O(1) lookup.
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let exposed_in_era = exposed_map.get(era)
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.map(|set| set.contains(who))
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.unwrap_or(false);
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```
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**substrate-0002:** Replace list scan with sorted `Vec` + `binary_search`:
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```rust
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// Before
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authorities.iter().any(|a| a == id) // O(n)
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// After
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// CWE-407 fix: binary_search on sorted Vec for O(log n) instead of O(n) scan.
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authorities.binary_search(id).is_ok()
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```
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## Patch
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`defects/substrate/patch/substrate-0001-0002-staking-consensus-hashset.patch`
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## What We Ask
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1. Confirm receipt and assign a GitHub Security Advisory or issue reference.
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2. Validate the patch against your staking and consensus test suites.
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3. Assess CVE eligibility — substrate-0001 measured at 38,550× in staking hot path.
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4. Coordinate a disclosure date — we are targeting 90 days from first contact.
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Contact: see cover email. This brief is confidential until coordinated disclosure.
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