Incident Overview
An attacker exploited BurgerSwap using flash loans and a fake token, resulting in a loss of $7.2 million.
The attacker initiated a flash swap of 6k WBNB ($2M) from PancakeSwap, which was then swapped for 92k BURGER on BurgerSwap. The attacker then created a non-standard BEP-20 token and formed a new trading pair with BURGER. Using this pair, the attacker swapped 100 fake tokens for 4.4k WBNB, and then swapped 45k BURGER for another 4.4k WBNB.
The attacker then swapped 493 WBNB for 108.7k BURGER on BurgerSwap, before finally repaying the flash swap.
Incident Report
Protocol Information
Market Context at Time of Hack
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.
What Auditors Should Check
If you're auditing a protocol with similar architecture to BurgerSwap, these are the critical security checks that could have prevented this incident (May 2021).
- Verify all logic paths related to Flashloan Reentrancy Attack / Flash Loan Attack are guarded by proper access controls and input validation - see the Flash Loans Attacks attack class for patterns
- Check that all state-changing functions follow the Checks-Effects-Interactions (CEI) pattern to prevent reentrancy and logic ordering bugs
- 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 TrialRelated Attack Classes
The technique used in this hack maps to these vulnerability classes in our security curriculum:
Proof-of-Concept Exploits
On-Chain Evidence & References
- Twitter/X Alert https://twitter.com/Mudit__Gupta/status/1398156036574306304
Sources & References
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Reference https://rekt.news/burgerswap-rekt/
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Learn to Prevent the Next BurgerSwap
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