Security incident · 2025-11-03
Balancer V2
According to the public DefiLlama incident dataset, Balancer V2 (Ethereum, Arbitrum, Base, Polygon, Sonic, Optimism) suffered a security incident on 2025-11-03, with about $128.0M reported lost.
| Date | 2025-11-03 |
|---|---|
| Reported loss | $128.0M |
| Chain | Ethereum, Arbitrum, Base, Polygon, Sonic, Optimism |
| Target type | DeFi Protocol |
| Technique class | Token & Share Accounting |
| Technique | Rounding Error |
| Bridge incident | No |
| Within 2025 | #3 by loss that year, 4.7% of all reported losses that year |
How this kind of attack works
The contract's bookkeeping was wrong, for example the conversion between shares and assets, so the attacker redeemed far more than they put in.
Would a pre-payment check have helped
Accounting and share-math bugs are contract-layer problems for code audits.
Other incidents with the same technique
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- Euler V12023-03-13 · $197.0M
- Compound V22021-09-29 · $147.0M
- Tectonic2026-08-30 · $124.5M
- Elrond2022-06-05 · $113.0M
- Uranium Finance2021-04-28 · $57.2M