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

// 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

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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, above them a coverage table carrying a verdict for every pattern
4. Provide fixes for each identified issue
5. Check weight calculations and origin validation

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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.

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.

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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

# 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

# Find direct arithmetic
rg " \+ |\+=| - |-=| \* |\*=| / |/=" pallets/

# Should find checked/saturating alternatives instead
rg "checked_add|checked_sub|checked_mul|checked_div" pallets/
rg "saturating_add|saturating_sub|saturating_mul" 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

Step 6: Origin & Privilege Review

# Find privileged operations
rg "ensure_signed" pallets/ | grep -E "pause|emergency|admin|force|sudo"

# 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

Step 8: Report Coverage

Report on every pattern in §5, whether or not it turned anything up. This skill has no Finding Template, so the table opens the report and the findings follow it, with all 7 rows present:

#	Pattern	Verdict	Evidence
1	Arithmetic Overflow	found	src/lib.rs:212 -- + on BalanceOf<T> in do_transfer
2	Don't Panic
3	Weights and Fees
4	Verify First, Write Last
5	Unsigned Transaction Validation
6	Bad Randomness
7	Bad Origin

Each verdict is one of:

• found — cite file:line and write the finding up in full after the table.
• clear — the pattern applies to this pallet and the pallet handles it. Name the macro, origin check, or arithmetic method you searched for, so a reader can repeat the search.
• n/a — the pattern cannot apply here. Give the reason in one clause ("this pallet accepts no unsigned transactions"). Not having looked is not n/a. Note that pattern 4 is version-scoped (pre-v0.9.25): say which runtime version the pallet targets rather than dropping the row.

A table with fewer than 7 rows is an incomplete scan and must be reported as one. A row whose Verdict cell is empty is incomplete in the same way: row 1 above is filled in to show the shape, and every row is filled in the same way before the report is done. Seven clear verdicts is a result a reader can act on. A report that covers three patterns and says nothing about the other four reads exactly like a clean pallet, and that is the failure this table exists to prevent.

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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

// 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

# 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

# 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

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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/

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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
• Coverage table emitted with all 7 rows, each carrying a verdict of found, clear or n/a with a reason

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11. Rationalizations to Reject

• "The pallet is small, so most patterns obviously don't apply." Obvious to whom? An n/a costs one clause and makes the judgment reviewable. Silence records nothing, and a reader cannot tell it apart from not having checked.
• "It compiles without warnings, so the arithmetic is fine." Release builds wrap silently. + on a Balance is pattern 1 whether or not the compiler said anything, and debug assertions do not run on a production node.
• "I checked the patterns that matter for this pallet." Deciding which patterns matter is the scan, not a precondition for starting it. Rank by severity after the table is complete, not by leaving rows out.
• "No findings, so there is nothing to report." A zero-finding scan still emits the full coverage table. That table is the deliverable: it is what distinguishes a pallet that was examined from one that was glanced at.
• "ensure_signed is an origin check." It establishes that someone signed, not that the right someone did. Pattern 7 is about which origin is required, and ensure_signed where ensure_root belongs passes this rationalization while failing the check.
• "The weight is benchmarked, so it's correct." Benchmarks measure the path they exercise. A dispatchable whose worst case depends on storage size or an unbounded loop is pattern 3 even with a benchmark attached.