Bent Finance Hack

TOTAL LOST $1.8M
Medium User Balances Manually Updated / Other ethereum

Summarize with AI

ChatGPT Perplexity Claude Grok
Affected Chain ethereum Incident surface
Recovered - No recovery reported
All-Time Rank #694 By amount stolen
Auditors 1 Prior security audit

Incident Overview

Quick Summary

Bent Finance became a victim to an insider's exploit. The exploiter extracted approx. $USD 1.75M in value from the project.

Details of the Exploit

Bent Finance is a staking and farming platform that optimizes returns from the curve protocol.

The Bent Finance team was in the process of migrating its contracts to a multisig wallet hereby effectively addressing internal security issues. Only days before the migration a developer on the team hardcoded the maximum fees on the crv and mim pool contracts to 17%. The developer also introduced a malicious smart contract that enabled the deployer to hardcode users balances.  The exploiter proceeded to assign an enormous balance to his account, far exceeding the TVL of Bent Finance. Subsequently, the developer launched a new smart contract in order to cover his tracks. Through these mechanisms the dishonest deployer was pledged rewards in the billions by the smart contracts.

All of the above mentioned proxy updates completely changed the functionality of the smart contracts and would not have been possible a couple of days later after the multisig migration would have concluded. The crooked deployer proceeded to withdraw 513k cvxcrv token and redirected them to a second address. With a third address, the deployer removed liquidity and transferred received theETH to the exploiter #2 address:

https://etherscan.io/tx/0x0a91dfc9…1e2a25

https://etherscan.io/tx/0x2bda5f87…963120

The second exploiter address washed the funds through Tornado.cash.

Block Data Reference

The addresses, marked as the exploiters:

#1: https://etherscan.io/address/0xd23cfffa…686d1f

#2: https://etherscan.io/address/0x9e966a54…a6e468

#3: https://etherscan.io/address/0x71b1ee09…f1c21a

Bent Finance Crv Fi contract:

https://etherscan.io/address/0x270b6aff…049a86

Transaction of 263k cvxcrv from exploiter address 1 to exploiter address 2:

https://etherscan.io/tx/0x11961c4d…e219c5

Transaction of 250k cvxcrv from exploiter address 1 to exploiter address 2:

https://etherscan.io/tx/0x52d4d5a9…2b95be

Tornado.cash transactions:

https://etherscan.io/address/0x9e966a54…a6e468

Call updateVersion() of Bent cvxCRV token through ProxyAdmin at:

https://etherscan.io/tx/0xf711641e…9eadc7

Call updateVersion() of Bent MIM token, executing the backdoored line at:

https://etherscan.io/tx/0xd5e0d4ab…ae9fef

Bent Finance deployer upgrades the implementation of Bent cvxCRV token through ProxyAdmin at:

https://etherscan.io/tx/0xb37ffd77…f63a07

Incident Report

Protocol / Project Bent Finance
Date of Incident
Affected Chain(s) ethereum
Attack Technique User Balances Manually Updated / Other
Classification Protocol Logic / Yield Aggregator
Primary Source View Post-Mortem

Protocol Information

Protocol Type Yield
Affected Token BENT
Smart Contract Language Solidity
Official Website app.bentfinance.com/
Protocol Twitter/X @BENT_Finance
Team Anonymous
Source Code Unverified

Market Context at Time of Hack

Token Categories
Ethereum Ecosystem
Protocol Links
Discord

What the Attacker Needed to Succeed

Understanding the prerequisites for this type of attack helps auditors identify protocols that are most at risk and helps developers build better defenses.

Technical Knowledge Deep understanding of user balances manually updated / other and Solidity and EVM internals
Capital Required Seed capital to cover gas and initial position setup
On-Chain Access Ability to interact with ethereum smart contracts and deploy a custom exploit contract
Protocol Analysis Identification of the exploitable vulnerability in Bent Finance's contract logic - root cause: protocol logic / yield aggregator
Execution Speed Precise transaction ordering and timing to exploit the vulnerability within a single atomic block
Obfuscation Plan A strategy to launder and move stolen funds - typically through mixers, cross-chain bridges, or decentralized DEX swaps to resist tracing

What Auditors Should Check

Could this have been caught in audit? Likely — with a thorough User Balances Manually Updated / Other audit checklist and test coverage
Audited by Audit Report 1 — still lost $1.8M. Prior audits don't guarantee safety, especially after post-audit code changes.

If you're auditing a protocol with similar architecture to Bent Finance, these are the critical security checks that could have prevented this incident (December 2021).

  • Verify all logic paths related to User Balances Manually Updated / Other are guarded by proper access controls and input validation
  • Review privileged functions (owner, admin, governance) for potential abuse vectors - centralization risks should be documented and bounded with timelocks or multi-sigs

Master these auditing techniques with hands-on labs and real exploit scenarios in the Smart Contract Hacking course.

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Security Audit History

Sources & References

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