Visor Finance Hack

TOTAL LOST $530K
Low Other

Summarize with AI

ChatGPT Perplexity Claude Grok
Affected Chain 2021 Incident surface
Recovered - No recovery reported
All-Time Rank #985 By amount stolen
Auditors 1 Prior security audit

Incident Overview

The attacker:

https://etherscan.io/address/0x8efab89b…7774b2

The transaction behind the attack:

https://etherscan.io/tx/0x69272d8c…c1ff3f

Exploited contract:

https://etherscan.io/address/0xc9f27a50…da14ef#code

The problem:

Deposit function calls delegatedTransferERC20 function on any contract from parameter "from" without any restrictions, this function call opens ability for reenter target contract. After calling delegatedTransferERC20 function deposit was called a second time. This lead to minting double share amount. In addition, there is no check for the "from" parameter, so the called contract can do nothing, and the function can be called with any value for visrDeposit parameter.

Minted share tokens were withdrawn and exchanged for VISAR tokens. Then the attacker sold them in liquidity pair on Uniswap and deposited them into Tornado Cash mixer:

https://etherscan.io/address/0x8efab89b…7774b2#tokentxns

https://bloxy.info/txs/calls_from/0x8efab89b…7774b2?signature_id=994162&smart_contract_address_bin=0x722122df…5b6967

Incident Report

Protocol / Project Visor Finance
Date of Incident
Attack Technique Other
Classification Yield Aggregator
Primary Source View Post-Mortem #1 View Post-Mortem #2 View Post-Mortem #3

Protocol Information

Protocol Type Lending
Affected Token VISR
Official Website www.visor.finance/
Protocol Twitter/X @visorfinance
Team Anonymous
Source Code Unverified

Market Context at Time of Hack

Token Categories
BNB Chain Ecosystem
Protocol Links
Reddit

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 other and Solidity and EVM internals
Capital Required Seed capital to cover gas and initial position setup
On-Chain Access Ability to interact with smart contracts and deploy a custom exploit contract
Protocol Analysis Identification of the exploitable vulnerability in Visor Finance's contract logic - root cause: 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 Other audit checklist and test coverage
Audited by Audit Report 1 — still lost $530K. Prior audits don't guarantee safety, especially after post-audit code changes.

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

  • Verify all logic paths related to 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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