How much was lost in the SunnyDefi finance hack?

The SunnyDefi finance hack resulted in — in losses on August 26, 2021.

What attack technique was used in the SunnyDefi finance exploit?

The SunnyDefi finance exploit utilized Rugpull. 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.

SunnyDefi finance Hack

TOTAL LOST —

Aug 26, 2021 Rugpull binance

Affected Chain binance Incident surface

Recovered - No recovery reported

Same Technique 865 Total incidents

Protocol Type Lending Target category

Incident Overview

Sonne Finance is a decentralized lending protocol for individuals, institutions and protocols to access financial services. It is a permissionless, open source and Optimistic protocol serving users on Optimism. Users can deposit their assets, use them as collateral and borrow against them

Incident Report

Protocol / Project SunnyDefi finance

Date of Incident August 26, 2021

Affected Chain(s) binance

Attack Technique Rugpull

Classification Token

Primary Source View Post-Mortem

Protocol Information

Protocol Type Lending

Affected Token SUNNY

Official Website sunnydefi.finance/

Protocol Twitter/X @SonneFinance

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 rugpull and Solidity and EVM internals

Capital Required Seed capital to cover gas and initial position setup

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

Protocol Analysis Identification of the exploitable vulnerability in SunnyDefi finance's contract logic - root cause: token

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? Hard to catch — private key / OpSec failures are outside smart contract audit scope

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

Verify all logic paths related to Rugpull 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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Sources & References

01
Source 1 https://bscscan.com/token/0x64a8f4387d522658b72a955dc9d30b2b589d352c

Threat Assessment

Severity Level

UNKNOWN

Attack Vector Rugpull
Root Cause Token
Year 2021

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