# Balancer V2 Pools Drained via Faulty Smart Contract Access Control Logic ∞ Security

**Published:** 2025-11-11
**Categories:** Security

---

![A futuristic white and metallic modular apparatus is depicted against a dark background, featuring interconnected cylindrical components. The leftmost module showcases a transparent blue circular front panel with intricate internal circuitry and a central glowing ring](https://incrypthos.com/wp-content/uploads/2025/09/cryptographic-hashing-algorithm-node-synchronization-system.jpeg)

![A vibrant blue, intricately structured translucent form dominates the foreground, set against a blurred background of metallic cylindrical and gear-like components. The detailed blue lattice appears to flow and connect, highlighting its complex internal structure and reflective surfaces](https://incrypthos.com/wp-content/uploads/2025/09/Smart-Contract-Execution-Flow-within-Blockchain-Infrastructure-Nodes.jpeg)

## Briefing

A severe security incident on the Balancer V2 protocol resulted in the unauthorized draining of assets from Composable Stable Pools across multiple chains. The primary consequence is a significant loss of liquidity and a subsequent depeg of associated tokens, eroding user trust in the protocol’s core vault architecture. Forensic analysis confirms the total financial impact exceeded $128 million, stemming from a single, critical [access control](https://incrypthos.com/news/access-control/) vulnerability.

![A transparent blue, possibly resin, housing reveals internal metallic components, including a precision-machined connector and a fine metallic pin extending into the material. This sophisticated assembly suggests a specialized hardware device designed for high-security operations](https://incrypthos.com/wp-content/uploads/2025/09/secure-hardware-wallet-interface-digital-asset-custody-module.jpeg)

## Context

The DeFi ecosystem operates with an inherent and persistent risk profile, where the complexity of pooled assets and multi-chain deployments expands the attack surface. Protocols utilizing shared vault logic, like Balancer V2, are perpetually exposed to access control vulnerabilities, where a single logic error can compromise all integrated pools. This incident leveraged the known risk of unaudited or insufficiently validated [internal withdrawal](https://incrypthos.com/news/internal-withdrawal/) functions within complex smart contract systems.

![A polished metallic cylindrical component, featuring a dark nozzle and a delicate golden wire, precisely interacts with a vibrant blue, translucent fluid. The fluid appears to be actively channeled and shaped by the mechanism, creating a dynamic visual of flow and processing](https://incrypthos.com/wp-content/uploads/2025/09/defi-protocol-orchestrating-digital-asset-liquidity-flow.jpeg)

## Analysis

The attacker exploited a faulty logic check within Balancer V2’s manageUserBalance function, which failed to properly validate the sender’s authorization for internal operations. This flaw allowed the execution of the UserBalanceOpKind.WITHDRAW_INTERNAL operation, effectively impersonating legitimate users to empty the vault’s internal balances. The attacker successfully bypassed the intended security mechanism by manipulating the check between msg.sender and a user-supplied op.sender. The root cause is a systemic failure in access control, demonstrating that a single point of failure in a core function can lead to total asset compromise across the entire [protocol](https://incrypthos.com/news/protocol/).

![The image features a detailed close-up of intertwined, tubular structures. One prominent element is translucent deep blue, revealing internal circuit-like patterns and small, embedded metallic rectangular components, while other structures are smooth, reflective silver](https://incrypthos.com/wp-content/uploads/2025/09/decentralized-ledger-interconnection-digital-asset-cryptographic-network-architecture.jpeg)

## Parameters

- **Total Funds Lost** ∞ $128 Million – The maximum estimated value of [assets](https://incrypthos.com/news/assets/) drained across all affected chains and pools.

- **Vulnerability Type** ∞ [Access Control Flaw](https://incrypthos.com/news/access-control-flaw/) – The specific smart contract logic error allowing unauthorized withdrawals.

- **Affected Function** ∞ manageUserBalance – The core [contract](https://incrypthos.com/news/contract/) function containing the exploitable logic check.

- **Recovery Metric** ∞ 15% – The approximate percentage of funds recovered by white-hat efforts and DAO emergency actions.

![The image displays a composition of metallic, disc-like components and intricate, translucent blue organic forms, all interconnected by flowing silver tubes. The background is a gradient of grey tones, providing a clean, high-tech aesthetic](https://incrypthos.com/wp-content/uploads/2025/09/decentralized-network-architecture-data-flow-cryptographic-security-protocol-ecosystem.jpeg)

## Outlook

Immediate mitigation requires all protocols with similar vault-and-pool architectures to conduct an emergency review of all internal withdrawal and balance management functions. The second-order effect is a heightened contagion risk for all forks and protocols that inherited the vulnerable Balancer V2 codebase, necessitating immediate isolation or hard forks. This event establishes a new security best practice ∞ the [formal verification](https://incrypthos.com/news/formal-verification/) of all access control logic in shared vault systems must become a non-negotiable auditing standard to prevent single-point-of-failure exploits.

![A sophisticated, futuristic mechanical apparatus features a brightly glowing blue central core, flanked by two streamlined white cylindrical modules. Visible internal blue components and intricate structures suggest advanced technological function and data processing](https://incrypthos.com/wp-content/uploads/2025/09/decentralized-network-node-executing-smart-contract-consensus-protocols.jpeg)

## Verdict

**This nine-figure [exploit](https://incrypthos.com/news/exploit/) confirms that systemic access control flaws in shared DeFi vault architectures remain the single greatest operational risk to institutional capital and must be addressed through mandatory formal verification.**

Smart contract exploit, Access control flaw, Internal withdrawal, Decentralized finance, Multi-chain vulnerability, Liquidity pool drain, Vault logic error, Systemic risk, On-chain forensics, Code vulnerability, Asset security, Protocol governance, Emergency mitigation, DeFi audit failure, Financial primitives Signal Acquired from ∞ <a href="https://decrypt.co/347173/balancer-exploited-128-million-across-ethereum-chains-berachain-halts?utm_source=incrypthos.com&utm_medium=referral&utm_campaign=noo-engine.com" target="_blank" rel="nofollow">decrypt.co</a> 

## Micro Crypto News Feeds

<a href="https://incrypthos.com/news/access-control/" class="glossary-item-box">

## access control 

Definition ∞ Access control dictates who or what can view or use resources within a digital system. </a><a href="https://incrypthos.com/news/internal-withdrawal/" class="glossary-item-box">

## internal withdrawal 

Definition ∞ An internal withdrawal moves digital assets between accounts on the same platform. </a><a href="https://incrypthos.com/news/protocol/" class="glossary-item-box">

## protocol 

Definition ∞ A protocol is a set of rules governing data exchange or communication between systems. </a><a href="https://incrypthos.com/news/assets/" class="glossary-item-box">

## assets 

Definition ∞ A digital asset represents a unit of value recorded on a blockchain or similar distributed ledger technology. </a><a href="https://incrypthos.com/news/access-control-flaw/" class="glossary-item-box">

## access control flaw 

Definition ∞ An access control flaw permits unauthorized users to perform actions they should not be able to. </a><a href="https://incrypthos.com/news/contract/" class="glossary-item-box">

## contract 

Definition ∞ A 'Contract' is a set of rules and code that automatically executes when predefined conditions are met. </a><a href="https://incrypthos.com/news/formal-verification/" class="glossary-item-box">

## formal verification 

Definition ∞ Formal verification is a mathematical technique used to prove the correctness of software or hardware systems. </a><a href="https://incrypthos.com/news/exploit/" class="glossary-item-box">

## exploit 

Definition ∞ An exploit refers to the malicious utilization of a security flaw or vulnerability within a protocol, smart contract, or application to gain unauthorized access, steal assets, or disrupt operations. </a>

**Tags:** [Emergency Mitigation](https://incrypthos.com/news/emergency-mitigation/), [Protocol Governance](https://incrypthos.com/news/protocol-governance/), [Protocols](https://incrypthos.com/news/protocols/), [Code Vulnerability](https://incrypthos.com/news/code-vulnerability/), [Mitigation](https://incrypthos.com/news/mitigation/), [Smart Contract](https://incrypthos.com/news/smart-contract/)	

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![A faceted crystalline structure, resembling a digital gem, is centrally positioned within a complex, futuristic circuit board. This visual metaphor represents the core of blockchain technology, perhaps symbolizing a native token or a critical consensus mechanism. The surrounding robotic components and intricate pathways suggest the sophisticated infrastructure and security protocols underpinning decentralized finance DeFi and smart contract execution. It embodies the immutable and transparent nature of distributed ledger systems, hinting at the digital asset's intrinsic value and its role in the broader crypto ecosystem.](https://incrypthos.com/wp-content/uploads/2025/09/Decentralized-Ledger-Technology-Embodiment-Secure-Cryptographic-Protocol-Nexus.jpeg)

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- 
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![A close-up reveals two intertwined toroidal structures. One, a smooth metallic silver, represents a foundational blockchain architecture or a secure protocol layer. The other, transparent and filled with vibrant, turbulent blue liquid, symbolizes dynamic digital asset flow, perhaps representing liquidity pools or smart contract execution within a decentralized ledger technology. This intricate interaction highlights cross-chain communication and interoperability, essential for Layer-2 scaling solutions and efficient transaction throughput across a validator network, emphasizing robust network security and data integrity.](https://incrypthos.com/wp-content/uploads/2025/09/blockchain-interoperability-protocol-dynamic-liquidity-flow.jpeg)

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![Two circular metallic objects feature transparent blue segments revealing intricate internal mechanisms. Visible gears, ruby bearings, and a balance wheel suggest precision engineering. This visual metaphor represents the robust cryptographic primitives and complex consensus mechanisms underpinning distributed ledger technology. The transparency highlights on-chain verifiable transactions and the integrity of smart contract logic, crucial for institutional-grade digital asset management.](https://incrypthos.com/wp-content/uploads/2025/09/blockchain-protocol-internal-mechanisms-tokenized-asset-transparency.jpeg)

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**Tags:** [Access Control](https://incrypthos.com/news/access-control/), [Access Control Flaw](https://incrypthos.com/news/access-control-flaw/), [Asset](https://incrypthos.com/news/asset/), [Asset Security](https://incrypthos.com/news/asset-security/), [Assets](https://incrypthos.com/news/assets/), [Audit Failure](https://incrypthos.com/news/audit-failure/), [Code Vulnerability](https://incrypthos.com/news/code-vulnerability/), [Contract](https://incrypthos.com/news/contract/), [Decentralized Finance](https://incrypthos.com/news/decentralized-finance/), [DeFi](https://incrypthos.com/news/defi/), [DeFi Audit Failure](https://incrypthos.com/news/defi-audit-failure/), [Emergency Mitigation](https://incrypthos.com/news/emergency-mitigation/), [Exploit](https://incrypthos.com/news/exploit/), [Financial](https://incrypthos.com/news/financial/), [Financial Primitives](https://incrypthos.com/news/financial-primitives/), [Formal Verification](https://incrypthos.com/news/formal-verification/), [Governance Emergency](https://incrypthos.com/news/governance-emergency/), [Internal Withdrawal](https://incrypthos.com/news/internal-withdrawal/), [Liquidity](https://incrypthos.com/news/liquidity/), [Liquidity Pool](https://incrypthos.com/news/liquidity-pool/), [Liquidity Pool Drain](https://incrypthos.com/news/liquidity-pool-drain/), [Logic Error](https://incrypthos.com/news/logic-error/), [Mitigation](https://incrypthos.com/news/mitigation/), [Multi-Chain](https://incrypthos.com/news/multi-chain/), [Multi-Chain Vulnerability](https://incrypthos.com/news/multi-chain-vulnerability/), [On-Chain Forensics](https://incrypthos.com/news/on-chain-forensics/), [Protocol](https://incrypthos.com/news/protocol/), [Protocol Governance](https://incrypthos.com/news/protocol-governance/), [Protocols](https://incrypthos.com/news/protocols/), [Risk](https://incrypthos.com/news/risk/), [Security](https://incrypthos.com/news/security/), [Smart Contract](https://incrypthos.com/news/smart-contract/), [Smart Contract Exploit](https://incrypthos.com/news/smart-contract-exploit/), [Systemic Risk](https://incrypthos.com/news/systemic-risk/), [Vault Logic Error](https://incrypthos.com/news/vault-logic-error/), [Vulnerability](https://incrypthos.com/news/vulnerability/)

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---

**Original URL:** https://incrypthos.com/security/balancer-v2-pools-drained-via-faulty-smart-contract-access-control-logic/
