PolyDEX Hack

TOTAL LOST $511K
Low Other

Summarize with AI

ChatGPT Perplexity Claude Grok
Affected Chain 2021 Incident surface
Recovered - No recovery reported
All-Time Rank #996 By amount stolen
Auditors 1 Prior security audit

Incident Overview

The attacker's address:

https://polygonscan.com/address/0x8a0a1eb0…907c6c

The transaction behind the attack:

https://polygonscan.com/tx/0x6b3f0576…ebe3a2

The attacker performed the re-entrance attack on the Token Locker smart contract. The contract itself does not have an issue with standard ERC20, but since the PLX token is ERC777 standard, there will be tokenReceived() callback event every time method transfer() triggered. The attacking smart contract deployed by the hacker has included the unlockAll() trigger repeatedly (40 times) in the event, so he was able to unlock more than the amount he locked in before.

The attacker:

- locked 15,711,384 PLX in the Locker, received 15,711,384 fPLX

- unlocked all 15,711,384 fPLX from the Locker, received 1,184,289 PLX

- in the tokenReceived() called unlockAll() function

- repeated previous step 40 times.

Stolen tokens were sold on USDC, which then were bridged on Ethereum:

https://polygonscan.com/tx/0xe02124b1…6bd1ad

Incident Report

Protocol / Project PolyDEX
Date of Incident
Attack Technique Other
Classification Exchange (DEX)
Primary Source View Post-Mortem

Protocol Information

Protocol Type Dexs
Affected Token PLX
Official Website www.polydex.fi/
Protocol Twitter/X @PolyDexFi
Team Anonymous
Source Code Unverified

Market Context at Time of Hack

Token Categories
Decentralized Exchange (DEX) Token DeFi Ethereum Ecosystem Polkadot DEX Polkadot Ecosystem Polkastarter OKX Ventures Portfolio
Protocol Links
GitHub

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 PolyDEX's contract logic - root cause: exchange (dex)
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 $511K. Prior audits don't guarantee safety, especially after post-audit code changes.

If you're auditing a protocol with similar architecture to PolyDEX, these are the critical security checks that could have prevented this incident (June 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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