How Does Balancer V2 Work?
Balancer V2 is the legacy version of the Balancer decentralized exchange, still running across multiple blockchains with $74M in deposits. It allows flexible pool designs with custom asset ratios. However, V2 suffered a devastating $128M exploit in November 2025 from a math error in its stable pool code, causing over half its TVL to flee. V2 is being phased out in favor of V3, but legacy pools remain live and carry elevated risk.
TVL
$37M
Sector
DEX
Risk Grade
C-
Value Grade
D-
Core Mechanisms
DEX/AMM/Weighted
Weighted pools with customizable asset ratios (e.g., 80/20, 60/20/20)
Standard weighted pool AMM since 2020. Allows arbitrary asset ratios beyond the typical 50/50 split. Core V2 functionality.
DEX/AMM/Stable
Composable stable pools for pegged assets — the pool type exploited in the November 2025 hack
Standard stable pool pattern. The V2 composable stable pool invariant contained a rounding error that was exploited for $128M in November 2025. This specific pool type carries elevated risk on V2.
DEX/AMM/Boosted
Boosted pools connecting idle liquidity to yield-bearing protocols
Boosted pools route idle liquidity to external yield sources (Aave, Euler). Introduces composability risk from yield-source protocol dependencies.
Governance/veToken
veBAL: vote-escrowed BAL for governance and fee distribution
Standard veToken pattern adopted from Curve. Lock BAL for up to 1 year for veBAL. Governs gauge emissions and protocol parameters.
Emissions/Gauge
Gauge voting for BAL emission allocation across pools
Standard gauge voting for emission direction. Similar to Curve's gauge system.
Flash-Loan/Native
Flash loans from the Balancer vault
The V2 vault provides flash loans. Standard pattern since 2020. Flash loans can be used to amplify attack vectors.
Cross-Chain/Multi-Deployment
V2 deployed across Ethereum, Polygon, Arbitrum, Gnosis, and other chains
Multi-chain V2 deployments remain live even as V3 launches. Each chain's V2 deployment carries independent risk and may not receive security updates.
How the Pieces Interact
The November 2025 exploit demonstrated that rounding errors in the composable stable pool math can be weaponized to drain pools. Despite prior audits, this class of precision bugs went undetected. Remaining V2 composable stable pools may harbor similar issues.
V2 contracts across multiple chains cannot be upgraded (immutable). Known vulnerability classes persist until all liquidity migrates to V3. Multi-chain coordination of security responses is slow, leaving some deployments exposed for extended periods.
The V2 vault's flash loan facility can amplify attacks against pool invariant bugs. An attacker can borrow large amounts, manipulate pool state, extract value, and repay within a single transaction — exactly the pattern used in the November 2025 exploit.
Boosted pools route idle liquidity to external protocols. If an external yield source is exploited (e.g., Euler hack in March 2023 affected Balancer boosted pools), LP depositors in boosted pools suffer losses from external protocol failures.
The $128M exploit created a governance crisis. veBAL holders must now govern both V2 wind-down and V3 transition simultaneously. Governance fatigue and fractured community attention could lead to suboptimal security decisions.
What Could Go Wrong
- $128M exploit in November 2025 via rounding error in composable stable pool invariant — the largest DEX exploit at that scale in DeFi history
- Legacy V2 contracts remain deployed across multiple chains with known vulnerability classes; migration to V3 is incomplete
- 58% TVL collapse post-exploit ($775M to $258M) signals deep erosion of protocol trust and institutional confidence
Second V2 Exploit Across Multiple Chains
ModerateTrigger: A second critical vulnerability is discovered in V2 contracts (e.g., in weighted pools or vault logic), and exploited across multiple chains before liquidity can be migrated
- 1.Security researcher or attacker discovers a new critical vulnerability in V2 pool or vault contracts — V2 deployments across Ethereum, Polygon, Arbitrum, and other chains are all vulnerable simultaneously
- 2.Attacker exploits the vulnerability on the chain with highest V2 TVL first, then moves to other chains — Multi-chain drain of V2 pools within hours; $50-74M at risk across remaining V2 TVL
- 3.Community loses all remaining confidence in Balancer V2; even V3 trust is damaged by association — BAL token crashes 60-80%; veBAL governance becomes dysfunctional as locked token value evaporates
- 4.Protocols and integrations that still rely on V2 pools face emergency migration pressure — Balancer ecosystem faces existential crisis; V3 adoption is set back as institutional partners reassess relationship
Risk Profile at a Glance
Overall: C- (51/100)
Lower score = safer