How much was lost in the Belt Finance hack?

The Belt Finance hack resulted in $6.3M in losses on May 29, 2021.

What attack technique was used in the Belt Finance exploit?

The Belt Finance exploit utilized Flashloan Price Oracle Attack / Flash Loan Attack. Understanding this attack vector is critical for smart contract auditors and developers building secure DeFi protocols.

How can developers prevent similar smart contract attacks?

Preventing smart contract hacks requires a combination of secure coding practices, thorough security audits, and understanding common attack vectors like reentrancy, oracle manipulation, and access control flaws. Smart Contract Hacking (SCH) provides hands-on training to help developers and auditors identify and prevent vulnerabilities before deployment.

Belt Finance Hack

TOTAL LOST $6.3M

Medium May 29, 2021 Flashloan Price Oracle Attack / Flash Loan Attack binance bsc

Affected Chain binance 2 chains affected

Recovered - No recovery reported

All-Time Rank #392 By amount stolen

Auditors 1 Prior security audit

Incident Overview

Quick Summary

Belt Finance suffered a flash loan attack exploiting the Ellipsis strategy, resulting in a loss of approximately $6.3 million.

Details of the Exploit

The attacker manipulated the value of a token within a liquidity pool by borrowing cryptocurrency using a flash loan. They exploited a bug in the integration of the Ellipsis strategy within Belt, causing an imbalance in the 3eps pool by swapping BUSD to USDT. This imbalance led to an overestimation of the value of Belt Finance's vault shares.

The attacker then withdrew BUSD from the Venus strategy, receiving more tokens than they should have, and providing a profit. The attack was repeated seven times, each iteration providing a profit of about $1 million.

Block Data Reference

The attacker's address:

https://etherscan.io/address/0xd8428836…208f50

The contract used to perform the attack:

https://etherscan.io/address/0x1c932902…2f3cee#code

Example of the attack execution:

https://etherscan.io/tx/0xeefc22f2…490f7b

Victim contract:

https://etherscan.io/address/0x41B85670…57cf49#code

Transaction of stolen funds transferred to the external wallet:

https://etherscan.io/tx/0xa8a61f77…1e775e

This is classified as a Flash Loans Attacks, Oracle Manipulation & Price Manipulation . Compare similar hacks →

Incident Report

Protocol / Project Belt Finance

Date of Incident May 29, 2021

Affected Chain(s) binance bsc

Attack Technique Flashloan Price Oracle Attack / Flash Loan Attack

Classification Ecosystem / Exchange (DEX),Yield Aggregator

Primary Source View Post-Mortem

Protocol Information

Protocol Type Yield

Affected Token BELT

Smart Contract Language Solidity

Official Website belt.fi/

Protocol Twitter/X @BELT_Finance

Team Anonymous

Source Code Unverified

Market Context at Time of Hack

Token Categories

DeFi Yield Farming BNB Chain Ecosystem

Protocol Links

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 flashloan price oracle attack / flash loan attack and Solidity and EVM internals

Capital Required Flash loan capital (borrowed atomically, zero upfront cost)

On-Chain Access Ability to interact with binance, bsc smart contracts and deploy a custom exploit contract

Protocol Analysis Identification of the exploitable vulnerability in Belt Finance's contract logic - root cause: ecosystem / exchange (dex),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? Yes — skilled auditors routinely flag Flashloan Price Oracle Attack / Flash Loan Attack vulnerabilities in code review

Audited by Audit Report 1 — still lost $6.3M. Prior audits don't guarantee safety, especially after post-audit code changes.

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

Verify all logic paths related to Flashloan Price Oracle Attack / Flash Loan Attack are guarded by proper access controls and input validation - see the Flash Loans Attacks attack class for patterns
Audit oracle price feeds for manipulation risks - ensure time-weighted average prices (TWAPs) or multi-source aggregators are used, not spot prices
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

Audit Report 1 Report

Related Attack Classes

The technique used in this hack maps to these vulnerability classes in our security curriculum:

See all Flash Loans Attacks examples →

Flash Loans Attacks Oracle Manipulation & Price Manipulation

Sources & References

01
Source 1 https://rekt.news/belt-rekt/
02
Reference https://medium.com/belt-finance/may-29-incident-report-865d20cc46ca

Threat Assessment

Severity Level

MEDIUM

Attack Vector Flashloan Price Oracle Attack / Flash Loan Attack
Root Cause Ecosystem / Exchange (DEX),Yield Aggregator
Year 2021

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