apegurus/erc4626-exchange-rate-manipulation

<!-- Source: BailSec audit reports (CC0) -->

ERC4626 Exchange Rate Manipulation Vulnerabilities

Overview

This pattern targets vault systems that rely on ERC-4626 share/asset conversion, especially when those conversions are consumed by lending, collateral, or routing logic. Attackers manipulate the apparent exchange rate (or timing of its update) so victims mint too few shares, borrow against mispriced collateral, or absorb bad debt. The exploit usually combines one of: flash liquidity, share supply edge cases, stale accounting, rounding asymmetry, or permissive user-specified share parameters.

The core failure is trusting conversion outputs as if they were immutable and manipulation-resistant under adversarial flow ordering.

Common Patterns

• User-facing functions accept shares as input without robust slippage/min-out protection.
• Vault share price can be inflated/deflated between preview and execution.
• First-user or low-liquidity states create nonlinear price jumps.
• Protocol treats ERC-4626 collateral as safe despite supply concentration and flash accessibility.

Detection Heuristics

• Trace every use of convertToShares/Assets and preview* into borrow limits, liquidation, and accounting updates.
• Check for same-tx manipulability of totalAssets or effective share supply.
• Verify min-out controls for both assets and shares on deposit/withdraw flows.
• Stress-test empty, near-empty, and first-deposit states with fuzzed ordering.

Examples from Audits

• Share-price inflation path where a victim specifying share quantity could be induced to supply more assets than intended.
• ERC-4626 collateral market where flash-loan control of share supply enabled bad-debt creation through exchange-rate distortion.
• Vault inflation scenario where fee accrual and conversion math created attacker-favorable rounding for later users.

Remediation

Require explicit user slippage bounds on both assets and shares. Add anti-manipulation checks that compare pre/post conversion expectations and reject large deltas within the same transaction context. Introduce bootstrap protections for first deposits (seed shares, dead shares, or guarded initialization). For lending integrations, gate collateral eligibility, cap concentration, and add oracle or TWAP defenses around vault share pricing. Finally, test conversion invariants under adversarial ordering and flash-capital assumptions.