Incident Overview
On May 18th, Feminist Metaverse’s FmToken contract was exploited for about 1838 BNB.
Attacker transaction: https://bscscan.com/tx/0xfdc90e06…8b320d
Attacker address: https://bscscan.com/address/0xaaA1634D…f1eF50
Attacker contract: https://bscscan.com/address/0x0B8d7522…Bca10F
Victim contract: https://bscscan.com/address/0x84352874…0df0f1
Exploit step by step:
1) Attacker directly receives FmToken that is not credited to the liquidity pool using skim function of the SakeSwapPair contract.
2) Attacker transfers 10 FmTokens tokens into an attacking contract to prepare for a subsequent attack.
3) Attacker calls the attack contract, where it cyclically transfer FmToken to the attacker's address, thereby triggering the operation of transferring tokens from the FmToken contract to SakeSwapPair and, finally, transferring them to the attacker's address through the skim function.
4) Multiple transfers of small amounts of FM token to their own address using the created attacker contract 0x0B8d…a10F.
5) Since the FmToken contract balance has reached the standard 150,000 token for transferring to SakeSwapPair, each transfer triggers line 920 to increase the balance of FmToken to SakeSwapPair. SakeSwapPair thus has a difference between token balance and reserve SakeSwapPair thus has a difference between token balance and reserve.
6) Then attacker calls the skim() function in SakeSwapPair to extract the difference in token balance to his own address.
7) Using PancakeSwap attacker swapped FmToken for BNB
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 Feminist Metaverse, these are the critical security checks that could have prevented this incident (May 2022).
- 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
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- Certik Report
Sources & References
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