MonoX Hack

TOTAL LOST $31.4M
High #169 All-Time Swap Function Exploit / Other ethereum polygon

Summarize with AI

ChatGPT Perplexity Claude Grok
Affected Chain ethereum 2 chains affected
Recovered - No recovery reported
All-Time Rank #169 By amount stolen
Auditors 4 Prior security audits

Incident Overview

Quick Summary

Monoswap contracts on Polygon and Ethereum were exploited due to a flaw in the swapTokenForExactToken() function, allowing the attackers to inflate the value of the MONO token and drain other tokens from the pool.

Details of the Exploit

The attackers exploited a weakness in the swapTokenForExactToken() function in the Monoswap contract, using the same token as tokenIn and tokenOut. This resulted in the price of the MONO token being artificially inflated. The attackers then used this inflated token to swap out almost all of the other tokens in the pool.

Stolen funds:

- 5.7M MATIC ($10.5M)

- 3.9k WETH ($18.2M)

- 36.1 WBTC ($2M)

- 1.2k LINK ($31k)

- 3.1k GHST ($9.1k)

- 5.1M DUCK ($257k)

- 4.1k MIM ($4.1k)

- 274 IMX ($2k)

Block Data Reference

The attacker's addresses:

Polygon: https://polygonscan.com/address/0xecbe385f…953258

Ethereum: https://etherscan.io/address/0xecbe385f…953258

Transactions behind the attack:

Polygon: https://polygonscan.com/tx/0x5a03b9c0…004d5d

Ethereum: https://etherscan.io/tx/0x9f14d093…f5f299

Incident Report

Protocol / Project MonoX
Date of Incident
Affected Chain(s) ethereum polygon
Attack Technique Swap Function Exploit / Other
Classification Protocol Logic / Exchange (DEX)
Primary Source View Post-Mortem

Protocol Information

Protocol Type Dexs
Affected Token MONO
Smart Contract Language Solidity
Official Website monox.finance/
Protocol Twitter/X @MonoXFinance
Team Anonymous
Source Code Unverified

Market Context at Time of Hack

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 swap function exploit / 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, polygon smart contracts and deploy a custom exploit contract
Protocol Analysis Identification of the exploitable vulnerability in MonoX's contract logic - root cause: protocol logic / 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 Swap Function Exploit / Other audit checklist and test coverage
Audited by Audit Report 1, Audit Report 2, Audit Report 3, Audit Report 4 — still lost $31.4M. Prior audits don't guarantee safety, especially after post-audit code changes.

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

  • Verify all logic paths related to Swap Function Exploit / 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

Proof-of-Concept Exploits

1 PoC available
poc-exploits - monox
$ MonoX Finance Price Manipulation

On-Chain Evidence & References

Sources & References

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