How much was lost in the Poly Network hack?

The Poly Network hack resulted in $611M in losses on August 10, 2021.

What attack technique was used in the Poly Network exploit?

The Poly Network exploit utilized Access Control Exploit / Other. 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.

Poly Network Hack

TOTAL LOST $611M

Critical #21 All-Time Aug 10, 2021 Access Control Exploit / Other bsc ethereum polygon

Affected Chain bsc 3 chains affected

Recovered $602.2M 98.6% returned

All-Time Rank #21 By amount stolen

Auditors 1 Prior security audit

Incident Overview

Quick Summary

Polynetwork was hacked for $602M. The attacker used Proxy smart contracts on 3 chains.

Details of the Exploit

Polynetwork is a DeFi platform. The project was hacked for 602,189,570 $USD in various assets. The attacker used unverified Proxy smart contracts on 3 chains. After the hack, the attacker who is called "Mr. White Hat", connected to the PolyNetwork team, and returned all stolen funds.

Security experts said it was likely the attacker realized it would be difficult for them to launder the money and cash out since all transactions are recorded on the blockchain.

Block Data Reference

Malicious smart contracts:

1. https://bscscan.com/address/0x7cea671d…15c87b#code

2. https://polygonscan.com/address/0xabd7f7b8…d7d5c9#code

3. https://etherscan.io/address/0x838bf9e9…928270#code

The owner of the Proxy contract on ETH (which was used in the attack) is another bytecoded contract (https://etherscan.io/address/0x5a51E2eb…44d2Eb) with the EOA ownership.

EOA was previously funded by OKEX exchange's Hot Wallet:

https://etherscan.io/tx/0xe864536a…71be02

Attacker’s addresses:

Polygon:

https://polygonscan.com/address/0x5dc3603c…663214

Binance Smart Chain:

https://bscscan.com/address/0x0d6e286a…b32c71

Ethereum:

https://etherscan.io/address/0xc8a65fad…589963

The attacker started to approve USDC and BUSD tokens in order to deposit them into Ellipsis stablecoin pool:

https://bscscan.com/tx/0x5fe51028…91fce8

https://bscscan.com/tx/0x4c6eaf4b…ab1ba4

Deposited into Ellipsis stablecoin pool ($32,107,136.29 BUSD and $87,602,010.73 USDC):

https://bscscan.com/tx/0x6768b484…cc9b4e

The attacker started to approve USDC and DAI tokens in order to deposit them into Curve stablecoin pool:

https://etherscan.io/tx/0x6c0b80dd…99683d

https://etherscan.io/tx/0xa51979f5…4b52ea

Deposited into Curve stablecoin pool ($671,156.42 DAI and $96,299,898.44 USDC):

https://etherscan.io/tx/0xbc54deb4…b14485

remove_liquidity_one_coin() - $96,643,770.34 DAI was removed backed to the exploiter’s address:

https://etherscan.io/tx/0x2465d4cf…63c1a1

Stolen funds:

ETH chain:

616,082.58 Fei USD ($614,628)

26,109.06 WETH ($82,374,869)

33,431,197.73 USDT ($33,239,073)

14.47 renBTC ($656,638)

259,737,345,149.51 SHIB ($1,999,977)

43,023.75 UNI ($1,247,688)

673,227.94 DAI ($673,201)

1,032.12 WBTC ($46,946,198)

96,389,444.22 USDC ($96,375,567)

BSC chain:

32,107,854.11 BUSD ($32,105,564)

1,023.88 BTCB ($46,574,710)

26,629.15 ETH ($83,821,409)

87,603,373.77 USDC ($87,600,346)

Polygon chain:

85,089,610.911 USDC ($85,057,567)

This is classified as a Access Control Attacks . Compare similar hacks →

Incident Report

Protocol / Project Poly Network

Date of Incident August 10, 2021

Affected Chain(s) bsc ethereum polygon

Attack Technique Access Control Exploit / Other

Classification Protocol Logic / Other

Primary Source View Post-Mortem

Protocol Information

Protocol Type Bridge

Smart Contract Language Solidity

Official Website www.poly.network/

Protocol Twitter/X @PolyNetwork2

Team Anonymous

Source Code Verified On-Chain

Market Context at Time of Hack

Token Categories

Platform DeFi Scaling Ethereum Ecosystem

Protocol Links

GitHub 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 Operational-security tradecraft (phishing, malware, leaked seed phrases, or insider access) to obtain treasury signing authority

Capital Required Minimal capital - only enough to cover gas while draining the compromised accounts

On-Chain Access Valid signing authority over the compromised wallets / multisig signers, allowing direct transfer of funds or stake authorization

Target Reconnaissance Identification of Poly Network's high-value treasury accounts and the authority / multisig structure controlling them

Execution Speed Speed to drain the compromised accounts before the team detects the breach and revokes signing authority or freezes the assets

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 Access Control Exploit / Other audit checklist and test coverage

Audited by Audit Report 1 — still lost $611M. Prior audits don't guarantee safety, especially after post-audit code changes.

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

Verify all logic paths related to Access Control Exploit / Other are guarded by proper access controls and input validation - see the Access Control Attacks attack class for patterns
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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Funds Recovery

98.6%

Recovered

$602.2M

Net Loss

8554000

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 Access Control Attacks examples →

Access Control Attacks

Proof-of-Concept Exploits

1 PoC available

poc-exploits - poly network

$ Poly Network Bridge, getting around modifier through cross-chain message

On-Chain Evidence & References

Reference https://rekt.news/polynetwork-rekt/
Post-Mortem https://slowmist.medium.com/the-root-cause-of-poly-network-being…
Block Explorer https://etherscan.io/tx/0xb1f70464bd95b774c6ce60fc706eb5f9e35cb5…
GitHub https://github.com/polynetwork/eth-contracts/tree/d16252b2b857ee…
Reference https://www.breadcrumbs.app/reports/671

Sources & References

01
Source 1 https://slowmist.medium.com/the-root-cause-of-poly-network-being…
02
Reference https://www.poly.network/

Threat Assessment

Severity Level

CRITICAL

Attack Vector Access Control Exploit / Other
Root Cause Protocol Logic / Other
Year 2021

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