# Users deposit assets to the vault but receives no strategy token in return

Notional Balancer vaults round BPT-to-strategy-token conversion to zero, so small depositors get no shares and their BPT is captured by existing holders.

- Payout: Contest reward
- Severity: high
- Program: Notional
- Credited: xiaoming90
- Disclosed: 2022-12-20
- Write-up quality: 6/10
- Original: https://github.com/sherlock-audit/2022-12-notional-judging/issues/16
- Library page: https://bugbountylibrary.com/r/sherlock%3A2022-12-notional%3AH-3
- Tags: domain:web3 impact:funds-loss kind:contest platform:sherlock sev:high tech:evm tech:solidity technique:source-review vuln:accounting-error vuln:precision-loss vuln:share-inflation

**Target:** Balancer TwoToken/Boosted3Token strategy vault deposit path
**Root cause:** _convertBPTClaimToStrategyTokens divides a 1e8-precision numerator by 1e18-precision denominator (or by totalBPTHeld scaled 1e18), so bptClaim below ~1e10 rounds down to zero strategy tokens; _deposit does not revert on zero mint.
**Steps:**
1. First depositor Alice deposits 10000 BPT; totalStrategyTokenGlobal=10000e8, totalBPTHeld=10000e18.
2. Bob deposits <1e10 BPT; `strategyTokenAmount = (bptClaim * 10000e8) / 10000e18` rounds to 0.
3. Bob receives 0 strategy tokens while his BPT is added to totalBPTHeld.
4. Alice withdraws all strategy tokens and redeems her BPT plus Bob's contributed BPT.
**How found:** Code reading of StrategyUtils._convertBPTClaimToStrategyTokens noticed numerator precision (1e8) far below denominator precision (1e18), then traced callers _deposit in Boosted3TokenPoolUtils and TwoTokenPoolUtils to confirm no zero-mint guard.
**Exploitation:** Attacker (or any small depositor) deposits a dust amount of BPT below the 1e10 threshold; minted strategy tokens round to zero, and the deposited BPT accrues to existing strategy token holders who can withdraw it.
**Insight:** When a share-mint formula mixes token precisions (1e8 internal vs 1e18 BPT), check the smallest deposit that still mints >=1 share; ERC4626-style vaults must revert on zero shares or dust deposits silently donate to existing holders.