economic-design-audit

Skill: Economic Design Audit (Solana)

Trigger Pattern: MONETARY_PARAMETER flag (required) Inject Into: Breadth agents (merged via M4 hierarchy) Finding prefix: [EDA-N] Rules referenced: S1, S4, S9, R2, R10, R13, R14

rate|rebase|supply|mint_authority|burn|emission|inflation|peg|price.*cap|price.*floor|
fee|reward.*rate|basis_points|bps

1. Parameter Boundary Analysis

For every monetary parameter setter (rate, fee, reward rate, emission, cap, floor, BPS values):

For each parameter: substitute min and max into ALL consuming instructions. Tag: [BOUNDARY:param=val -> outcome]

Solana-specific boundary checks:

• Does a parameter at MAX cause arithmetic overflow in u64/u128 operations? (Solana uses Rust's checked math by default in debug, but unchecked_* or release mode may overflow silently)
• Does a parameter at 0 cause division-by-zero panics? (Solana programs abort on panic -- entire transaction fails)
• Does a fee parameter at MAX (e.g., 10000 BPS = 100%) cause the user to receive 0 tokens?

2. Economic Invariant Identification

List all economic invariants the protocol must maintain:

For each setter: can changing this parameter break an invariant that user-facing instructions depend on? If yes -> finding.

Solana-specific invariants:

• Lamport conservation: Total lamports in program-owned accounts must be conserved across instructions (Solana runtime enforces this per-instruction, but multi-instruction sequences can violate economic invariants)
• Mint supply == sum of token account balances: If program has mint authority, can minting break supply-tracking invariants?
• Rent-exempt minimums: Parameter changes that reduce account sizes may violate rent-exempt requirements, making accounts eligible for garbage collection

3. Rate/Supply Interaction Matrix

For protocols with multiple monetary parameters that interact:

Check: can two independently-valid parameter settings combine to create an extreme or invalid economic state? (Rule 14 constraint coherence)

Example: reward_rate_bps = 5000 (valid alone) and boost_multiplier = 20 (valid alone) combine to effective_rate = 100000 BPS = 1000%, draining the reward vault in one epoch.

4. Fee Formula Verification at Normal Values

For every fee-related computation (fee calculation, fee deduction, fee distribution):

4a. Concrete Example Computation

Pick 3 representative fee rates (e.g., 1% = 100 BPS, 5% = 500 BPS, 10% = 1000 BPS) and trace through the actual code formula:

Tag: [BOUNDARY:fee_bps={val} → effective_rate={computed_rate}]

Red flags:

• Gross-up formulas: amount * MAX / (MAX - fee) charges effective rate of fee/(MAX-fee), not fee/MAX. At 5% this is 5.26%, not 5%. Document whether this is intentional.
• Fee-on-fee: Does fee A's output feed into fee B's input? If so, the combined effective rate is not simply A + B.
• Rounding direction: Does rounding favor the protocol or the user? For fee deductions, rounding UP (ceiling) favors the protocol.

4d. Fee-Base Consistency

For every fee computation, trace the base amount (the value the fee is computed on) through ALL subsequent code paths:

Methodology:

• Identify the variable used as fee base (e.g., amount, depositAmount)
• Trace that variable FORWARD from the fee computation to the end of the function
• If the variable is reduced (capped, downscaled, adjusted to remaining capacity, slippage-adjusted) AFTER the fee was computed → the fee was charged on a larger base than what was actually used
• Concrete test: If fee = amount * feeRate / MAX, then amount is reduced to leftover (e.g., remaining allocation), the user paid fee on amount but only leftover was processed - overcharge of fee * (1 - leftover/amount)

4b. Fee Interaction Matrix

For protocols with multiple fee types:

4c. Fee Impact on Share Price

If the protocol uses share-based accounting:

• After fee deduction: does the share price change?
• Does the fee mechanism create a spread between deposit and immediate withdrawal?
• Is the spread documented and within reasonable bounds?

5. Emission/Inflation Sustainability

For protocols with emission/inflation/reward distribution mechanics:

• What is the maximum emission rate over 1 epoch / 1 day / 1 year?
• Can emissions exceed the reward vault's SOL/token balance?
• Is there a supply cap on the mint? Can the authority bypass it?
• What happens when the reward vault is depleted? (revert? zero rewards? proportional reduction?)

6. Compute Unit Cost Modeling

For batch operations (mass distributions, multi-user updates, reward claims):

Solana-specific cost analysis:

• Per-transaction CU limit: 1,400,000 (1.4M)
• Per-instruction CU limit: 200,000 default (can request up to 1.4M with set_compute_unit_limit)
• Each account access: ~100-200 CU; each CPI: ~1000-5000 CU; each SHA256: ~100 CU per 64 bytes
• Priority fee dynamics: During congestion, priority fees can spike 100-1000x. Model whether time-sensitive operations (liquidations, rebalances, crank actions) remain economically viable during congestion.
• Can an attacker spam the network to make crank operations uneconomical?

7. Rent and Account Creation Economics

For protocols that create accounts on behalf of users:

Checks:

• Can an attacker force excessive account creation to drain protocol SOL? (e.g., creating reward claim accounts for non-existent users)
• Are account creation costs passed to users or absorbed by the protocol?
• If protocol absorbs cost: what is the total cost at design limit? Does the protocol hold enough SOL?
• Can accounts be closed to reclaim rent? Who receives the lamports?
• Account creation griefing: Can a user create Associated Token Accounts or PDA accounts that the protocol must later interact with, forcing the protocol to pay rent for accounts it did not intend to create?

Finding Template

**ID**: [EDA-N]
**Verdict**: CONFIRMED / PARTIAL / REFUTED / CONTESTED
**Step Execution**: (see checklist below)
**Rules Applied**: [S1:___, S4:___, S9:___, R2:___, R10:___, R13:___, R14:___]
**Severity**: Critical/High/Medium/Low/Info
**Location**: programs/{program}/src/{file}.rs:LineN
**Title**: {parameter boundary violation / invariant break / economic unsustainability}
**Description**: {specific issue with code reference and numerical example}
**Impact**: {quantified at worst-state operational parameters -- Rule 10}

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Step Execution Checklist (MANDATORY)

If any step skipped, document valid reason (N/A, single parameter, no emissions, no account creation).