{"investigation":{"slug":"balancer","entity_name":"Balancer","trust_score":42,"severity_base":null,"score_modifier":10,"confidence":0.82,"status":"published","content_type":"investigation","summary":"Balancer is a decentralized automated market maker (AMM) protocol on Ethereum, founded in 2018 by Fernando Martinelli and Mike McDonald, that allows multi-token liquidity pools with customizable weighting. The protocol has suffered six documented security incidents between 2020 and 2025, resulting in cumulative losses exceeding $140 million, including a catastrophic $128 million exploit in November 2025 caused by an arithmetic precision flaw in Composable Stable Pool contracts. Despite multiple audits by major firms including Trail of Bits, OpenZeppelin, and Certora, systemic smart contract vulnerabilities and a highly complex protocol architecture have repeatedly exposed user funds to loss.","sections":[{"content":"Balancer is a non-custodial portfolio manager and automated market maker (AMM) protocol deployed on Ethereum and multiple EVM-compatible chains. Unlike traditional AMMs that require two-asset 50/50 pools, Balancer permits pools of up to eight assets with customizable weighting ratios, functioning as a generalization of the constant-product invariant. The protocol was conceived as an R&D project at BlockScience in 2018, and Balancer Labs raised $3 million in a March 2020 funding round before launching the V1 mainnet. Balancer V2 launched in April 2021, introducing a unified vault architecture that consolidated liquidity and separated pool logic from asset management. The protocol's native governance token, BAL, launched in June 2020, with 25 million tokens allocated to founders, investors, and developers and 65 million reserved for liquidity providers. BAL holders can vote-lock tokens in an 80/20 BAL/ETH pool to participate in protocol governance. As of November 2025, prior to its largest exploit, Balancer's total value locked was approximately $442 million.","heading":"Protocol Overview","sources":[{"url":"https://cryptopotato.com/balancer-protocol-guide/","name":"cryptopotato.com","type":"other","credibility":3},{"url":"https://coinmarketcap.com/academy/article/what-is-balancer","name":"coinmarketcap.com","type":"other","credibility":3},{"url":"https://getblock.io/blog/bringing-perfect-balance-to-amms-story-of-balancer-bal/","name":"getblock.io","type":"other","credibility":3}],"severity":"medium"},{"content":"On June 28, 2020, an attacker exploited a compatibility flaw between Balancer's smart contracts and so-called deflationary tokens — ERC-20 tokens that impose a transfer fee on each movement of funds. The attack targeted the Statera (STA) and STONK token pools. The attacker borrowed 104,331 WETH via a flash loan from dYdX, then executed a series of rapid swaps that progressively drained STA from a Balancer pool. Because STA charges a 1% burn fee on each transfer, only 99 tokens arrive in the pool for every 100 sent, creating a discrepancy between the contract's internal token records and actual balances. The attacker then called the gulp() function to reset the pool's internal accounting to reflect the near-zero STA balance, then swapped all pool assets out using the negligibly small remaining STA quantity at a massively inflated implied price. Total losses were approximately $523,600. A bug bounty report had previously identified the deflationary token incompatibility, and Balancer paid the bounty and reimbursed affected users. This incident highlighted that Balancer's pool design did not account for transfer-fee tokens.","heading":"June 2020: Deflationary Token Flash Loan Exploit (~$523,000)","sources":[{"url":"https://blog.peckshield.com/2020/06/28/balancer/","name":"blog.peckshield.com","type":"other","credibility":3},{"url":"https://decrypt.co/33937/hacker-steals-500k-crypto-balancer-pool","name":"decrypt.co","type":"other","credibility":3},{"url":"https://www.quadrigainitiative.com/casestudy/balancerdeflationhack.php","name":"quadrigainitiative.com","type":"other","credibility":3}],"severity":"medium"},{"content":"On March 13, 2023, Euler Finance suffered a $197 million flash loan exploit. Balancer's bb-e-USD (Euler Boosted USD) pool was collaterally damaged because it held Euler eTokens as underlying assets. Approximately $11.9 million worth of tokens from the bb-e-USD pool were transmitted to Euler during the attack. Balancer's emergency subDAO paused the pool and placed it in recovery mode at 11:00 UTC on March 13, but over 65% of the pool's total value locked had already been lost by that point. A secondary issue emerged: a bug in Balancer's user interface prevented remaining liquidity providers from withdrawing their residual funds, though Balancer subsequently deployed a corrected UI allowing recovery. This incident illustrated the systemic composability risk inherent in DeFi, where a vulnerability in one protocol can cascade losses into dependent protocols without any direct flaw in the secondary protocol's code.","heading":"March 2023: Indirect Losses from Euler Finance Exploit (~$11.9 Million)","sources":[{"url":"https://cointelegraph.com/news/euler-attack-causes-locked-tokens-losses-in-11-defi-protocols-including-balancer","name":"cointelegraph.com","type":"other","credibility":3},{"url":"https://forum.balancer.fi/t/euler-hack-post-mortem/4490","name":"forum.balancer.fi","type":"other","credibility":3},{"url":"https://www.panewslab.com/en/articles/281ef9d5-31d1-4e7b-a9a6-267939b5cfa9","name":"panewslab.com","type":"other","credibility":3}],"severity":"medium"},{"content":"On August 22, 2023, Balancer publicly disclosed a critical vulnerability affecting certain V2 boosted pools — specialized liquidity pools that amplify yields by lending idle capital to external lending protocols such as Aave. The team estimated that approximately $2.8 million, representing roughly 0.42% of total TVL, remained at risk after most liquidity providers were notified to withdraw. By August 25, Balancer reported that 99.7% of the originally at-risk liquidity had been successfully withdrawn, with only approximately $565,199 remaining vulnerable. Despite these warnings, on August 27, 2023, attackers exploited the disclosed vulnerability via multiple flash loan transactions and drained over $2.1 million — a sum exceeding the amount Balancer had last estimated as still at risk. Blockchain security firm Beosin confirmed the attack involved flash loan manipulation of the affected boosted pool contracts across eight blockchain networks. The exploit demonstrated that even responsible disclosure with active user warnings cannot guarantee full fund protection if a subset of liquidity providers fails to withdraw in time. A white-hat researcher known as GothicShanon89238 had responsibly disclosed the underlying vulnerability through Immunefi and received a $130,000 bounty prior to the attack.","heading":"August 2023: Critical Vulnerability Disclosure and Exploit (~$2.1 Million)","sources":[{"url":"https://www.web3isgoinggreat.com/?id=balancer-exploit","name":"web3isgoinggreat.com","type":"other","credibility":3},{"url":"https://decrypt.co/154002/balancer-suffers-nearly-1m-exploit-team-urges-users-withdraw-funds","name":"decrypt.co","type":"other","credibility":3},{"url":"https://www.bitdegree.org/crypto/news/balancer-warns-users-of-vulnerability-in-some-pools-2-8m-still-at-risk","name":"bitdegree.org","type":"other","credibility":3},{"url":"https://cryptopotato.com/balancer-drained-for-almost-1m-days-after-disclosing-vulnerability/","name":"cryptopotato.com","type":"other","credibility":3}],"severity":"medium"},{"content":"On September 19, 2023, Balancer's frontend website was compromised via a social engineering attack on EuroDNS, the domain registrar responsible for the .fi top-level domain used by Balancer. Blockchain security firm SlowMist identified the method as a Border Gateway Protocol (BGP) hijacking attack, in which the attacker corrupted internet routing tables to redirect users from the legitimate Balancer website to a malicious phishing front-end. Users who connected their wallets to the fraudulent interface and approved transactions had funds drained. Assets were stolen across multiple networks including Ethereum, Arbitrum, Optimism, Polygon, Base, and Avalanche. Total stolen value was approximately $253,044. Balancer's decentralized autonomous organization worked to recover the domain, restoring it by approximately 5:45 pm UTC on September 20, 2023. This attack did not exploit any vulnerability in Balancer's smart contracts, but rather the off-chain domain infrastructure. This is the incident the initial investigation brief describes as a 'September 2023 oracle manipulation attack' — the actual vector was DNS/BGP hijacking, not oracle manipulation.","heading":"September 2023: DNS and BGP Hijacking of Frontend (~$253,000)","sources":[{"url":"https://decrypt.co/197953/balancer-frontend-hit-by-dns-attack-over-250k-stolen","name":"decrypt.co","type":"other","credibility":3},{"url":"https://cointelegraph.com/news/balancer-social-engineering-attack-dns-provider-frontend-hijack","name":"cointelegraph.com","type":"other","credibility":3},{"url":"https://slowmist.medium.com/analysis-of-balancer-bgp-hijacking-incident-40adb6b285b5","name":"slowmist.medium.com","type":"other","credibility":3},{"url":"https://www.theblock.co/post/251970/balancer-dns-attack-frontend","name":"theblock.co","type":"other","credibility":3}],"severity":"medium"},{"content":"On June 2, 2024, Velocore — a decentralized exchange built as a fork of Balancer's constant-product market maker architecture — suffered an exploit resulting in approximately $6.8 million in losses across the Linea and zkSync Era networks. The root cause was faulty logic in the velocore__execute() function of the ConstantProductPool contract, which failed to verify that the caller was the authorized Vault contract. Attackers used this vulnerability to simulate large withdrawals, driving a feeMultiplier variable to extreme values causing fee calculation overflow. A subsequent flash-loan-backed withdrawal then minted an abnormally large quantity of LP tokens, which were used to drain pool assets. While Velocore is a separate protocol and its losses do not accrue directly to Balancer protocol users, the incident illustrates the risks of deploying Balancer's complex pool architecture in forked codebases without equivalent audit coverage, and underscores reputational and ecosystem risks for the Balancer codebase.","heading":"June 2024: Velocore Fork Exploit (~$6.8 Million)","sources":[{"url":"https://velocorexyz.medium.com/velocore-incident-post-mortem-6197020ec3e9","name":"velocorexyz.medium.com","type":"other","credibility":3},{"url":"https://rekt.news/velocore-rekt/","name":"rekt.news","type":"other","credibility":3},{"url":"https://immunebytes.com/blog/velocore-finance-exploit-june-2-2024-detailed-analysis/","name":"immunebytes.com","type":"other","credibility":3},{"url":"https://smartcontractshacking.com/hacks/velocore-v2-hack-2024","name":"smartcontractshacking.com","type":"other","credibility":3}],"severity":"medium"},{"content":"On November 3, 2025, Balancer V2 suffered its largest-ever exploit, with approximately $128.64 million drained across six blockchain networks in under 30 minutes. The root cause was an arithmetic precision flaw in the _upscaleArray() function within Composable Stable Pool contracts. When token balances reached specific boundary thresholds (approximately 8-9 wei), Solidity's integer division caused material precision loss, causing the pool invariant D to be systematically underestimated. Attackers leveraged this flaw through a three-phase cycle repeated 65 times within atomic batchSwap transactions: first pushing pool balances to the critical rounding boundary, then executing small swaps to trigger invariant underestimation, then minting Balancer Pool Tokens (BPT) at the artificially suppressed price and immediately redeeming them at full value. Check Point Research noted the exploitation occurred primarily in a single attacker smart contract constructor call. Hypernative's monitoring systems detected abnormal swap patterns at approximately 07:46 UTC; PeckShield alerts confirmed roughly $70.8 million drained by approximately 08:00 UTC. Emergency pauses were activated across networks within 20 minutes, but a copycat attack appeared 53 minutes after the initial exploit. Balancer's total value locked dropped from approximately $442 million to approximately $182 million within 24 hours. Despite audits by OpenZeppelin, Trail of Bits, Certora, and ABDK Consulting — over a dozen reports since 2020 — the vulnerability was not previously identified. Partial recovery was achieved: StakeWise DAO recovered approximately $19 million in osETH and $1.7 million in osGNO under Balancer's Safe Harbor framework (BIP-726). The Berachain Foundation executed an emergency hard fork to trap stolen funds, and Sonic Labs froze attacker wallets. The attacker had used Tornado Cash to fund the initial transaction. Researchers noted the malicious smart contract contained console.log debugging statements, suggesting possible AI-assisted code generation.","heading":"November 2025: Rounding Error Exploit — Largest Incident (~$128 Million)","sources":[{"url":"https://research.checkpoint.com/2025/how-an-attacker-drained-128m-from-balancer-through-rounding-error-exploitation/","name":"research.checkpoint.com","type":"other","credibility":3},{"url":"https://www.halborn.com/blog/post/explained-the-balancer-hack-november-2025","name":"halborn.com","type":"other","credibility":3},{"url":"https://blog.trailofbits.com/2025/11/07/balancer-hack-analysis-and-guidance-for-the-defi-ecosystem/","name":"blog.trailofbits.com","type":"other","credibility":3},{"url":"https://www.theblock.co/post/377863/balancer-identifies-rounding-error-as-root-cause-of-multi-chain-defi-exploit","name":"theblock.co","type":"other","credibility":3},{"url":"https://www.certora.com/blog/breaking-down-the-balancer-hack","name":"certora.com","type":"other","credibility":3},{"url":"https://www.dlnews.com/articles/defi/balancer-suffers-128m-exploit-despite-multiple-audits/","name":"dlnews.com","type":"other","credibility":3}],"severity":"medium"},{"content":"Balancer has commissioned security audits from several prominent firms throughout its history, including OpenZeppelin, Trail of Bits, Certora, and ABDK Consulting, accumulating over a dozen audit reports since 2020. The protocol also maintains a bug bounty program through Immunefi, through which the August 2023 vulnerability was responsibly disclosed and awarded a $130,000 bounty. Despite this investment in security, the protocol has suffered six documented security incidents resulting in cumulative direct losses exceeding $140 million (not including the ~$11.9 million Euler-related indirect loss). The November 2025 exploit in particular demonstrated that arithmetic precision edge cases in ComposableStablePool contracts were not caught by any prior audit, a finding Trail of Bits described as guidance for the broader DeFi ecosystem. The complexity of Balancer's generalized invariant mathematics — which enables its multi-token, custom-weight pool design — appears to create audit surface that has repeatedly evaded detection. At least 27 Balancer V2 forks across multiple blockchains were reportedly still vulnerable following the November 2025 attack.","heading":"Audit History and Security Posture","sources":[{"url":"https://www.dlnews.com/articles/defi/balancer-suffers-128m-exploit-despite-multiple-audits/","name":"dlnews.com","type":"other","credibility":3},{"url":"https://blog.trailofbits.com/2025/11/07/balancer-hack-analysis-and-guidance-for-the-defi-ecosystem/","name":"blog.trailofbits.com","type":"other","credibility":3},{"url":"https://www.certora.com/blog/breaking-down-the-balancer-hack","name":"certora.com","type":"other","credibility":3},{"url":"https://cryptonews.com/exclusives/balancer-defi-protocol-may-have-lost-over-100-million-due-to-a-2023-bug/","name":"cryptonews.com","type":"other","credibility":3}],"severity":"medium"},{"content":"Balancer is governed by BAL token holders, who may participate by vote-locking tokens in a designated 80/20 BAL/ETH liquidity pool to receive veBAL (vote-escrowed BAL). The protocol's emergency subDAO has authority to pause pools in the event of detected attacks, a mechanism invoked during both the March 2023 Euler-related incident and the November 2025 exploit. In 2024, Balancer introduced its Safe Harbor framework (BIP-726), a formal legal structure under which white-hat responders may recover funds from attacked pools without liability, which proved effective in the November 2025 recovery efforts by StakeWise DAO. Token distribution at launch allocated 25% of the 100 million BAL supply to founders, investors, and developers, with the remaining 65 million earmarked for liquidity incentives. Observers have noted that the unified vault architecture of V2, while efficient for capital, also concentrates systemic risk — a single vulnerability can affect all pools on the platform simultaneously.","heading":"Governance and Decentralization","sources":[{"url":"https://cryptopotato.com/balancer-protocol-guide/","name":"cryptopotato.com","type":"other","credibility":3},{"url":"https://beincrypto.com/learn/balancer/","name":"beincrypto.com","type":"other","credibility":3},{"url":"https://www.ccn.com/education/crypto/balancer-exploit-smart-contracts-defi-blockchains-assets-impacted/","name":"ccn.com","type":"other","credibility":3}],"severity":"medium"}],"timeline":[{"date":"2018","event":"Balancer protocol research begins at BlockScience as an R&D project.","source":"","date_original":"2018-01-01"},{"date":"2020-03","event":"Balancer Labs raises $3 million in seed funding and launches Balancer V1 mainnet.","source":"","date_original":"2020-03-01"},{"date":"2020-06","event":"BAL governance token launches; 25 million tokens allocated to founders and investors, 65 million to liquidity providers.","source":"","date_original":"2020-06-01"},{"date":"2020-06-28","event":"Deflationary token flash loan exploit: attacker uses dYdX flash loan to drain STA and STONK pools. Approximately $523,600 stolen. Balancer reimburses affected users.","source":""},{"date":"2021-04","event":"Balancer V2 launches with unified vault architecture, separating pool logic from asset custody.","source":"","date_original":"2021-04-01"},{"date":"2023-03-13","event":"Euler Finance is exploited for $197 million. Balancer's bb-e-USD pool suffers approximately $11.9 million in indirect losses. Emergency subDAO pauses the pool.","source":""},{"date":"2023-08-22","event":"Balancer publicly discloses a critical vulnerability in V2 boosted pools and urges liquidity providers to withdraw funds. Approximately $2.8 million estimated at risk.","source":""},{"date":"2023-08-25","event":"Balancer reports 99.7% of at-risk liquidity withdrawn; approximately $565,199 still in vulnerable pools.","source":""},{"date":"2023-08-27","event":"Attackers exploit the disclosed August 22 vulnerability via flash loans, draining over $2.1 million across eight networks.","source":""},{"date":"2023-09-19","event":"Balancer frontend compromised via social engineering attack on EuroDNS registrar and BGP hijacking. Approximately $253,044 stolen from users who interacted with malicious front-end across six networks.","source":""},{"date":"2023-09-20","event":"Balancer DAO successfully recovers control of compromised domain by approximately 5:45 pm UTC.","source":""},{"date":"2024-06-02","event":"Velocore, a Balancer-fork DEX, is exploited for approximately $6.8 million on Linea and zkSync Era due to faulty logic in its ConstantProductPool contract.","source":""},{"date":"2025-11-03","event":"Balancer V2 suffers its largest-ever exploit: approximately $128.64 million drained across six blockchain networks in under 30 minutes via a rounding error in _upscaleArray() within ComposableStablePool contracts. Safe Harbor recoveries begin within hours.","source":""}],"sources_used":[{"url":"https://cryptopotato.com/balancer-protocol-guide/","name":"cryptopotato.com","type":"other","credibility":3},{"url":"https://coinmarketcap.com/academy/article/what-is-balancer","name":"coinmarketcap.com","type":"other","credibility":3},{"url":"https://getblock.io/blog/bringing-perfect-balance-to-amms-story-of-balancer-bal/","name":"getblock.io","type":"other","credibility":3},{"url":"https://blog.peckshield.com/2020/06/28/balancer/","name":"blog.peckshield.com","type":"other","credibility":3},{"url":"https://decrypt.co/33937/hacker-steals-500k-crypto-balancer-pool","name":"decrypt.co","type":"other","credibility":3},{"url":"https://www.quadrigainitiative.com/casestudy/balancerdeflationhack.php","name":"quadrigainitiative.com","type":"other","credibility":3},{"url":"https://cointelegraph.com/news/euler-attack-causes-locked-tokens-losses-in-11-defi-protocols-including-balancer","name":"cointelegraph.com","type":"other","credibility":3},{"url":"https://forum.balancer.fi/t/euler-hack-post-mortem/4490","name":"forum.balancer.fi","type":"other","credibility":3},{"url":"https://www.panewslab.com/en/articles/281ef9d5-31d1-4e7b-a9a6-267939b5cfa9","name":"panewslab.com","type":"other","credibility":3},{"url":"https://www.web3isgoinggreat.com/?id=balancer-exploit","name":"web3isgoinggreat.com","type":"other","credibility":3},{"url":"https://decrypt.co/154002/balancer-suffers-nearly-1m-exploit-team-urges-users-withdraw-funds","name":"decrypt.co","type":"other","credibility":3},{"url":"https://www.bitdegree.org/crypto/news/balancer-warns-users-of-vulnerability-in-some-pools-2-8m-still-at-risk","name":"bitdegree.org","type":"other","credibility":3},{"url":"https://cryptopotato.com/balancer-drained-for-almost-1m-days-after-disclosing-vulnerability/","name":"cryptopotato.com","type":"other","credibility":3},{"url":"https://decrypt.co/197953/balancer-frontend-hit-by-dns-attack-over-250k-stolen","name":"decrypt.co","type":"other","credibility":3},{"url":"https://cointelegraph.com/news/balancer-social-engineering-attack-dns-provider-frontend-hijack","name":"cointelegraph.com","type":"other","credibility":3},{"url":"https://slowmist.medium.com/analysis-of-balancer-bgp-hijacking-incident-40adb6b285b5","name":"slowmist.medium.com","type":"other","credibility":3},{"url":"https://www.theblock.co/post/251970/balancer-dns-attack-frontend","name":"theblock.co","type":"other","credibility":3},{"url":"https://velocorexyz.medium.com/velocore-incident-post-mortem-6197020ec3e9","name":"velocorexyz.medium.com","type":"other","credibility":3},{"url":"https://rekt.news/velocore-rekt/","name":"rekt.news","type":"other","credibility":3},{"url":"https://immunebytes.com/blog/velocore-finance-exploit-june-2-2024-detailed-analysis/","name":"immunebytes.com","type":"other","credibility":3},{"url":"https://smartcontractshacking.com/hacks/velocore-v2-hack-2024","name":"smartcontractshacking.com","type":"other","credibility":3},{"url":"https://research.checkpoint.com/2025/how-an-attacker-drained-128m-from-balancer-through-rounding-error-exploitation/","name":"research.checkpoint.com","type":"other","credibility":3},{"url":"https://www.halborn.com/blog/post/explained-the-balancer-hack-november-2025","name":"halborn.com","type":"other","credibility":3},{"url":"https://blog.trailofbits.com/2025/11/07/balancer-hack-analysis-and-guidance-for-the-defi-ecosystem/","name":"blog.trailofbits.com","type":"other","credibility":3},{"url":"https://www.theblock.co/post/377863/balancer-identifies-rounding-error-as-root-cause-of-multi-chain-defi-exploit","name":"theblock.co","type":"other","credibility":3},{"url":"https://www.certora.com/blog/breaking-down-the-balancer-hack","name":"certora.com","type":"other","credibility":3},{"url":"https://www.dlnews.com/articles/defi/balancer-suffers-128m-exploit-despite-multiple-audits/","name":"dlnews.com","type":"other","credibility":3},{"url":"https://cryptonews.com/exclusives/balancer-defi-protocol-may-have-lost-over-100-million-due-to-a-2023-bug/","name":"cryptonews.com","type":"other","credibility":3},{"url":"https://beincrypto.com/learn/balancer/","name":"beincrypto.com","type":"other","credibility":3},{"url":"https://www.ccn.com/education/crypto/balancer-exploit-smart-contracts-defi-blockchains-assets-impacted/","name":"ccn.com","type":"other","credibility":3}],"source_tags":[],"addresses":[],"reviewed":true,"reviewed_by":null,"model_used":"claude-sonnet-4-6","created_at":"2026-05-30T19:10:50.86316+00:00","updated_at":"2026-08-29T01:35:16.305+00:00"}}