How much was lost in the Onyx Protocol hack?

The Onyx Protocol hack resulted in $2.1M in losses on November 01, 2023.

What attack technique was used in the Onyx Protocol exploit?

The Onyx Protocol exploit utilized Flashloan Donate Function Logic Exploit / 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.

Onyx Protocol Hack

TOTAL LOST $2.1M

Medium Nov 01, 2023 Flashloan Donate Function Logic Exploit / Flash Loan Attack ethereum

Affected Chain ethereum Incident surface

Recovered - No recovery reported

All-Time Rank #633 By amount stolen

Auditors 1 Prior security audit

Incident Overview

Quick Summary

Onyx Protocol suffered a flash loan attack, exploiting a rounding issue, leading to a loss of approximately 2,149,772 USD worth 1,161.29 ETH.

Details of the Exploit

Onyx Protocol, a decentralized liquidity protocol, was exploited on November 1, 2023, through a flash loan attack. The attacker took advantage of a critical vulnerability in CompoundV2 forks, which caused a known rounding issue. To execute the exploit, the attacker took out a substantial flash loan in ETH, swiftly converting it to PEPE tokens and contributing PEPE tokens to a specific pool.

Due to precision loss, fewer shares were burned, enabling the withdrawal of assets. The exploit resulted in a loss of approximately 2,149,772 USD worth 1,161.29 ETH. The attacker has already laundered about 1,140 ETH (equivalent to 1.25 million USD) to the crypto mixing service Tornado Cash.

Block Data Reference

Attacker Addresses:

https://etherscan.io/address/0x085bDfF2…642BfF

https://etherscan.io/address/0x4C9C8661…330c98

https://etherscan.io/address/0x50839563…842706

Malicious Transaction:

https://etherscan.io/tx/0x27a3788d…899746

Malicious Contract:

https://etherscan.io/address/0x052Ad2f7…3fcEAa

TornadoCash Deposit Transactions:

https://etherscan.io/tx/0xf045dff0…ffd33e

https://etherscan.io/tx/0x3990b142…675e3c

https://etherscan.io/tx/0x17cc492f…ac2ca4

This is classified as a Flash Loans Attacks . Compare similar hacks →

Incident Report

Protocol / Project Onyx Protocol

Date of Incident November 01, 2023

Affected Chain(s) ethereum

Attack Technique Flashloan Donate Function Logic Exploit / Flash Loan Attack

Classification Ecosystem / Borrowing and Lending

Primary Source View Post-Mortem

Protocol Information

Protocol Type Lending

Affected Token XCN

Smart Contract Language Solidity

Official Website onyx.org/

Protocol Twitter/X @OnyxProtocol

Team Anonymous

Source Code Unverified

Market Context at Time of Hack

Token Categories

Collectibles & NFTs DeFi Gaming DAO Ethereum Ecosystem Yield Farming Governance Avalanche Ecosystem

Protocol Links

GitHub Discord

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 donate function logic exploit / 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 ethereum smart contracts and deploy a custom exploit contract

Protocol Analysis Identification of the exploitable vulnerability in Onyx Protocol's contract logic - root cause: ecosystem / borrowing and lending

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 Donate Function Logic Exploit / Flash Loan Attack vulnerabilities in code review

Audited by Audit Report 1 — still lost $2.1M. Prior audits don't guarantee safety, especially after post-audit code changes.

If you're auditing a protocol with similar architecture to Onyx Protocol, these are the critical security checks that could have prevented this incident (November 2023).

Verify all logic paths related to Flashloan Donate Function Logic Exploit / Flash Loan Attack are guarded by proper access controls and input validation - see the Flash Loans 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.

Free Trial

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

Sources & References

01
Source 1 https://twitter.com/decurityhq/status/1719657969925677161
02
Web Archive https://archive.ph/OdOwH
03
Reference https://twitter.com/DeDotFiSecurity/status/1719690524603425113?s=20

Threat Assessment

Severity Level

MEDIUM

Attack Vector Flashloan Donate Function Logic Exploit / Flash Loan Attack
Root Cause Ecosystem / Borrowing and Lending
Year 2023

Learn to Prevent the Next Onyx Protocol

The Onyx Protocol hack is one of many attacks that skilled auditors are trained to detect before deployment. Master real exploit patterns and defense techniques with hands-on Web3 security training.

Start Free Trial Browse Attack Library