substrate-vulnerability-scanner

by trailofbits

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SKILL.md About

---
name: substrate-vulnerability-scanner
description: Scans Substrate/Polkadot pallets for 7 critical vulnerabilities including arithmetic overflow, panic DoS, incorrect weights, and bad origin checks. Use when auditing Substrate runtimes or FRAME pallets.
---

# Substrate Vulnerability Scanner

## 1. Purpose

Systematically scan Substrate runtime modules (pallets) for platform-specific security vulnerabilities that can cause node crashes, DoS attacks, or unauthorized access. This skill encodes 7 critical vulnerability patterns unique to Substrate/FRAME-based chains.

## 2. When to Use This Skill

- Auditing custom Substrate pallets
- Reviewing FRAME runtime code
- Pre-launch security assessment of Substrate chains (Polkadot parachains, standalone chains)
- Validating dispatchable extrinsic functions
- Reviewing weight calculation functions
- Assessing unsigned transaction validation logic

## 3. Platform Detection

### File Extensions & Indicators
- **Rust files**: `.rs`

### Language/Framework Markers
```rust
// Substrate/FRAME indicators
#[pallet]
pub mod pallet {
    use frame_support::pallet_prelude::*;
    use frame_system::pallet_prelude::*;

#[pallet::config]
    pub trait Config: frame_system::Config { }

#[pallet::call]
    impl<T: Config> Pallet<T> {
        #[pallet::weight(10_000)]
        pub fn example_function(origin: OriginFor<T>) -> DispatchResult { }
    }
}

// Common patterns
DispatchResult, DispatchError
ensure!, ensure_signed, ensure_root
StorageValue, StorageMap, StorageDoubleMap
#[pallet::storage]
#[pallet::call]
#[pallet::weight]
#[pallet::validate_unsigned]
```

### Project Structure
- `pallets/*/lib.rs` - Pallet implementations
- `runtime/lib.rs` - Runtime configuration
- `benchmarking.rs` - Weight benchmarks
- `Cargo.toml` with `frame-*` dependencies

### Tool Support
- **cargo-fuzz**: Fuzz testing for Rust
- **test-fuzz**: Property-based testing framework
- **benchmarking framework**: Built-in weight calculation
- **try-runtime**: Runtime migration testing

---

## 4. How This Skill Works

When invoked, I will:

1. **Search your codebase** for Substrate pallets
2. **Analyze each pallet** for the 7 vulnerability patterns
3. **Report findings** with file references and severity
4. **Provide fixes** for each identified issue
5. **Check weight calculations** and origin validation

---

## 5. Vulnerability Patterns (7 Critical Patterns)

I check for 7 critical vulnerability patterns unique to Substrate/FRAME. For detailed detection patterns, code examples, mitigations, and testing strategies, see [VULNERABILITY_PATTERNS.md](resources/VULNERABILITY_PATTERNS.md).

### Pattern Summary:

1. **Arithmetic Overflow** ⚠️ CRITICAL
   - Direct `+`, `-`, `*`, `/` operators wrap in release mode
   - Must use `checked_*` or `saturating_*` methods
   - Affects balance/token calculations, reward/fee math

2. **Don't Panic** ⚠️ CRITICAL - DoS
   - Panics cause node to stop processing blocks
   - No `unwrap()`, `expect()`, array indexing without bounds check
   - All user input must be validated with `ensure!`

3. **Weights and Fees** ⚠️ CRITICAL - DoS
   - Incorrect weights allow spam attacks
   - Fixed weights for variable-cost operations enable DoS
   - Must use benchmarking framework, bound all input parameters

4. **Verify First, Write Last** ⚠️ HIGH (Pre-v0.9.25)
   - Storage writes before validation persist on error (pre-v0.9.25)
   - Pattern: validate → write → emit event
   - Upgrade to v0.9.25+ or use manual `#[transactional]`

5. **Unsigned Transaction Validation** ⚠️ HIGH
   - Insufficient validation allows spam/replay attacks
   - Prefer signed transactions
   - If unsigned: validate parameters, replay protection, authenticate source

6. **Bad Randomness** ⚠️ MEDIUM
   - `pallet_randomness_collective_flip` vulnerable to collusion
   - Must use BABE randomness (`pallet_babe::RandomnessFromOneEpochAgo`)
   - Use `random(subject)` not `random_seed()`

7. **Bad Origin** ⚠️ CRITICAL
   - `ensure_signed` allows any user for privileged operations
   - Must use `ensure_root` or custom origins (ForceOrigin, AdminOrigin)
   - Origin types must be properly configured in runtime

For complete vulnerability patterns with code examples, see [VULNERABILITY_PATTERNS.md](resources/VULNERABILITY_PATTERNS.md).

---

## 6. Scanning Workflow

### Step 1: Platform Identification
1. Verify Substrate/FRAME framework usage
2. Check Substrate version (v0.9.25+ has transactional storage)
3. Locate pallet implementations (`pallets/*/lib.rs`)
4. Identify runtime configuration (`runtime/lib.rs`)

### Step 2: Dispatchable Analysis
For each `#[pallet::call]` function:
- [ ] Arithmetic: Uses checked/saturating operations?
- [ ] Panics: No unwrap/expect/indexing?
- [ ] Weights: Proportional to cost, bounded inputs?
- [ ] Origin: Appropriate validation level?
- [ ] Validation: All checks before storage writes?

### Step 3: Panic Sweep
```bash
# Search for panic-prone patterns
rg "unwrap\(\)" pallets/
rg "expect\(" pallets/
rg "\[.*\]" pallets/  # Array indexing
rg " as u\d+" pallets/  # Type casts
rg "\.unwrap_or" pallets/
```

### Step 4: Arithmetic Safety Check
```bash
# Find direct arithmetic
rg " \+ |\+=| - |-=| \* |\*=| / |/=" pallets/

### Step 5: Weight Analysis
- [ ] Run benchmarking: `cargo test --features runtime-benchmarks`
- [ ] Verify weights match computational cost
- [ ] Check for bounded input parameters
- [ ] Review weight calculation functions

# Should use ensure_root or custom origins
rg "ensure_root|ForceOrigin|AdminOrigin" pallets/
```

### Step 7: Testing Review
- [ ] Unit tests cover all dispatchables
- [ ] Fuzz tests for panic conditions
- [ ] Benchmarks for weight calculation
- [ ] try-runtime tests for migrations

---

## 7. Priority Guidelines

### Critical (Immediate Fix Required)
- Arithmetic overflow (token creation, balance manipulation)
- Panic DoS (node crash risk)
- Bad origin (unauthorized privileged operations)

### High (Fix Before Launch)
- Incorrect weights (DoS via spam)
- Verify-first violations (state corruption, pre-v0.9.25)
- Unsigned validation issues (spam, replay attacks)

### Medium (Address in Audit)
- Bad randomness (manipulation possible but limited impact)

---

## 8. Testing Recommendations

### Fuzz Testing
```rust
// Use test-fuzz for property-based testing
#[cfg(test)]
mod tests {
    use test_fuzz::test_fuzz;

#[test_fuzz]
    fn fuzz_transfer(from: AccountId, to: AccountId, amount: u128) {
        // Should never panic
        let _ = Pallet::transfer(from, to, amount);
    }

#[test_fuzz]
    fn fuzz_no_panics(call: Call) {
        // No dispatchable should panic
        let _ = call.dispatch(origin);
    }
}
```

### Benchmarking
```bash
# Run benchmarks to generate weights
cargo build --release --features runtime-benchmarks
./target/release/node benchmark pallet \
    --chain dev \
    --pallet pallet_example \
    --extrinsic "*" \
    --steps 50 \
    --repeat 20
```

### try-runtime
```bash
# Test runtime upgrades
cargo build --release --features try-runtime
try-runtime --runtime ./target/release/wbuild/runtime.wasm \
    on-runtime-upgrade live --uri wss://rpc.polkadot.io
```

---

## 9. Additional Resources

- **Building Secure Contracts**: `building-secure-contracts/not-so-smart-contracts/substrate/`
- **Substrate Documentation**: https://docs.substrate.io/
- **FRAME Documentation**: https://paritytech.github.io/substrate/master/frame_support/
- **test-fuzz**: https://github.com/trailofbits/test-fuzz
- **Substrate StackExchange**: https://substrate.stackexchange.com/

---

## 10. Quick Reference Checklist

Before completing Substrate pallet audit:

**Arithmetic Safety (CRITICAL)**:
- [ ] No direct `+`, `-`, `*`, `/` operators in dispatchables
- [ ] All arithmetic uses `checked_*` or `saturating_*`
- [ ] Type conversions use `try_into()` with error handling

**Panic Prevention (CRITICAL)**:
- [ ] No `unwrap()` or `expect()` in dispatchables
- [ ] No direct array/slice indexing without bounds check
- [ ] All user inputs validated with `ensure!`
- [ ] Division operations check for zero divisor

**Weights & DoS (CRITICAL)**:
- [ ] Weights proportional to computational cost
- [ ] Input parameters have maximum bounds
- [ ] Benchmarking used to determine weights
- [ ] No free (zero-weight) expensive operations

**Access Control (CRITICAL)**:
- [ ] Privileged operations use `ensure_root` or custom origins
- [ ] `ensure_signed` only for user-level operations
- [ ] Origin types properly configured in runtime
- [ ] Sudo pallet removed before production

**Storage Safety (HIGH)**:
- [ ] Using Substrate v0.9.25+ OR manual `#[transactional]`
- [ ] Validation before storage writes
- [ ] Events emitted after successful operations

**Other (MEDIUM)**:
- [ ] Unsigned transactions use signed alternative if possible
- [ ] If unsigned: proper validation, replay protection, authentication
- [ ] BABE randomness used (not RandomnessCollectiveFlip)
- [ ] Randomness uses `random(subject)` not `random_seed()`

**Testing**:
- [ ] Unit tests for all dispatchables
- [ ] Fuzz tests to find panics
- [ ] Benchmarks generated and verified
- [ ] try-runtime tests for migrations