Thread by @k3mmio

Grim Finance(grim.finance) got hacked 2 hours ago
Estimated loss: $40mln

One of the attacking transactions: ftmscan.com/tx/0x19315e5b1…

Attack Analysis:
#FTM #ETH #BSC #GrimFinance #GrimExploit

1/4

1) Grab a Flashloan for XXX & YYY tokens (WBTC-FTM e.g.)
2) Add liquidity on SpiritSwap
3) Mint SPIRIT-LPs
4) call depositFor() in GrimBoostVault with token==ATTACKER, user==ATTACKER
5)Leverage token.safeTransferFrom for re-entrancy
6) goto (4)

2/4

7) In the last step on re-entrancy call depositFor() with token==SPIRIT-LP, user==ATTACKER
8) Amount of minted GB-XXX-YYY tokens is increased in every level of re-entrancy
9) Attacker ends up holding huge amount of GB-XXX-YYY tokens

3/4

10) Withdraw GB tokens and get more SPIRIT-LP tokens back
11) Remove liquidity and get more XXX and YYY tokens
12) Repay Flashloan

4/4