[BlockSec DeFi 攻擊分析系列之二] 傾囊相送：Sushiswap 手續費被盜_WETH

去中心化金融(DeFi)作為區塊鏈生態當紅項目形態，其安全尤為重要。從去年至今，發生了幾十起安全事件

BlockSec作為長期關注DeFi安全的研究團隊(https://blocksecteam

_toWETH函數：

function_toWETH(addresstoken)internalreturns(uint256){??//對于SUSHI，直接Sushimaker全部SUSHI轉給Bar??if(token==sushi){????uintamount=IERC20(token)

看出什么亮點了嗎？

SushiMaker里的轉賬邏輯都是：transfer(balanceOf(this))

我們可以分兩個階段來看convert的調用過程：第一個階段：在?convert函數中SushiMaker擁有的是?SLP，它通過burnbalanceOf(this)實現將全部SLP換成兩個底層代幣第二個階段：SushiMaker獲得了burn來的底層代幣，再拿burn得到的token去不同的交易池換wETH

你發現哪里有問題了嗎？我們來看第二階段的代碼_toWETH：注意兌換的邏輯為：

uintamount=IERC20(token).balanceOf(address(this));

所以這個balanceOf(address(this))真的只有在第一階段burn來的底層代幣嗎？Nononono~想一想，如果這里的token并不是底層代幣，而是一個SLP，會發生什么？

IERC20(SLP).balanceOf(address(this))是SushiMaker擁有的所有SLP，既包含剛剛burn出來的，也包含原本SushiMaker就有的

如果底層代幣是SLP，那第一階段burn的是什么？答案是?SLP的SLP！

還記得嗎？攻擊者的目標是將SushiMaker誘騙到其創建的惡意交易池中交易，這個SLP1/WETH池不恰好是攻擊者創建的，當攻擊者調用convert(SLP1,wETH)時，SushiMaker由于上面這一漏洞會將其全部的SLP1都到SLP1/WETH池中換取WETH——正中下懷

SLP/WETH池一般都是不存在的，或是深度很淺的。攻擊者其實也可以通過建立SLP1/SLP2來實現攻擊，但是這樣的話，還需要單獨為SLP1、SLP2建立SLP1/WETH，SLP2/WETH，不如直接一步到位

1.4RealWorld

管你看沒看懂，繼續看就完了下面我們來看看攻擊者在真實世界中到底做了什么吧？

攻擊者地址：0x1925e832C22522E0d9947eE4677120b2f28E4cD4(https://etherscan.io/address/0x1925e832c22522e0d9947ee4677120b2f28e4cd4)

一組攻擊包括很多筆交易，這里以對?MKR/WETH?池的攻擊為例：SwapExactETHforTokens:?0xa8c4edd85727dApprove：0xf1fdd4cf4d8aaAddLiquidityETH:0x7340edca1a17fApprove:0x41a33f0c91b7cAddLiquidityETH:0x896f412f15a7aTransfer:0x0e8a76bf7295dConvert:0x4947b4f075f8eSwapExactETHForTokens:0x5f37bb3b97341RemoteLiquidityETH:0xdff10159275e0SwapExactTokensForETH:0xb8889bbdeb478

攻擊者的一個完整的攻擊周期：

序章：攻擊準備

Step1：通過swapExactETHForTokens用一些ETH換取MKR，作為攻擊的啟動資金

Step2：將剛剛換到的MKR和ETH一起，向Sushi的MKR/wETH交易池中添加流動性，獲得該池的SLP(MKR/wETH)

Step3：將剛剛換到的SLP和ETH一起，向Sushi的SLP/wETH交易池中添加流動性，獲得新池的SLP(SLP/wETH)(后簡稱SLP')

Step4：將新生成的SLP'轉給SushiMaker

這步有什么意義呢？因為攻擊者后續會調用convert(SLP,wETH)，將SushiMaker.sol合約中存放的SLP'燃燒掉，換出SLP,wETH。如果SushiMaker.sol中沒有SLP'就沒法進行下去了

但是，實際復現過程中，我發現有沒有這步其實都影響不大。因為上一步addLiquidity(SLP,wETH)是，一方面會mint出SLP'給攻擊者，另一方面還會mint出一些SLP'給SushiMaker.sol，所以SushiMaker.sol中其實還是有一點SLP'的→現在攻擊者手里有SLP'，其實他有兩個不同的決策：

DOC上線首日最高漲幅900%:據官方消息，Dolphin coin上線交易所Bibull首日最高漲幅900%。Dolphin coin社區人數12000+，持幣地址10000+。Dolphin coin是完全由社區自發組織建設的實驗，并推出急速通縮型代幣DOC，每筆鏈上交易燃燒5%，其中3%投入流動性池，2%返還持幣人。[2021/5/11 21:48:38]

1.將SLP'轉給SushiMaker，這樣SushiMaker可以換出更多的SLP和wETH，下一步回到這個交易池將自己所有的SLP換成wETH2.不轉SLP'給SushiMaker，因為之前創建SLP/wETH這個池的時候會mint一點點SLP'給SushiMaker，所以還是可以通過調用convert將SushiMaker存的SLP都換成wETH

第一種方式中，使SushiMaker擁有的SLP'更多，會換出更多的SLP和wETH，使得池中的滑點更大，SushiMaker能虧的SLP就更多，但是如果SushiMaker中本身存的SLP就不多，SLP/wETH深度也不大時，其實結果差不太多，都是幾乎將SushiMaker搬空。總而言之，還是第一種方式更優，可以看出攻擊者其實是有精心考慮過的

高潮：攻擊SushiMaker

Step5：調用convert(SLP,wETH)，這一步中，SushiMaker會先將SLP'burn掉，換成SLP和wETH，再將自己所有的SLP都轉成wETH，問題在于?SLP/wETH這個池是由攻擊者創建的，池中的深度非常小，滑點極高，SushiMaker通過?swap將SLP換成wETH這步會血虧

尾聲：獲利

Step6：上一步中，SushiMaker在SLP/wETH這個池中血虧了大量的SLP，池中wETH巨值錢，此時攻擊者只需要調用swap用一點點wETH就可以幾乎將整個池子搬空

0x2.附錄

2.1本次事件相關的攻擊交易：[??{????"YFI/WETH":{??????"0x18be4ac177c5ada3522e3cafd6c40d750d4288a3a7b22e140521124074fed2ae":"SwapExactETHForTokens",??????"0xc8653ef0c4658acf3d44059babea07c62578769cac10176e61310f7af04e1597":"Approve",??????"0x18ed3e5efeec3e475501786541a4f7602340e5aa6bc6cbf24b9c9aa1062449ac":"AddLiquidityETH",??????"0x42d553b614d0a64ea2cfe95bf2a99d337c07f1b53ac4d7987966fc39817975e6":"Approve",??????"0x041463e755e91548b9d6dd1e61519b08f101ff96a44df969b33ee57996619a88":"AddLiquidityETH",??????"0x8a2d7926e50123459b7814c0e19b5ac59f7ce221cb5fa82f79d2c0c37ef7ef1f":"Transfer",??????"0xaa001ac10841c784954b0028192f0ea232bf84e390b964af98f1c49074ec4beb":"Convert",??????"0x08bbbeaf7cbd2649738812cf720042eb7ebe1411be2f7cf3ede41411dcbf8bc0":"SwapExactETHForTokens",??????"0x3952f24ef1e5dce37463edcf0f3902316131fb823d79946b96f2a2397a9cd25d":"RemoveLiquidityETH",??????"0x47c200fefd8c007d972b65b97dadf429c3e6e91359b7b49aaa66ee0fc4a555f4":"SwapExactTokensForETH"????},????"profit":"0.2558139ether"??},??{????"USDT/WETH":{??????"0x123ec6c44fa3baa70c66f583f8ee6bc6b6d2b4d39a1119ab8490d2c1120d4647":"Convert",??????"0x08bbbeaf7cbd2649738812cf720042eb7ebe1411be2f7cf3ede41411dcbf8bc0":"SwapExactETHForTokens",??????"0x42973ea279d0bda4222e4689709f86bdb12117dce14420f84f3e9cc6fd42ede2":"RemoteLiquidityETH",??????"0x30eab0a184f9a1ed6cee309754bb6536bd443fea567776a72b72f3ab911e0113":"SwapExactTokensForETH"????},????"profit":"0.1835604ether"??},??{????"MKR/WETH":{??????"0xa8c4edd85727d3d25401f0cbca1136982edb833f77ff0a93178b222063eb57a4":"SwapExactETHforTokens",??????"0xf1fdd4cf4d8aa073ff01876333cfeadeab2b87423664d1daa4cf36ad5e415587":"Approve",??????"0x7340edca1a17fc9e5a6587d6a89c0ed01c5d1f1d20cb19738ab993f6ef7b8b4d":"AddLiquidityETH",??????"0x41a33f0c91b7cd17edf888356dfb110d7744f593e432b54ec2f21aae19076aa0":"Approve",??????"0x896f412f15a7abb959c3c43b8cd9206720fc37f4eabeae336ba101670003e9db":"AddLiquidityETH",??????"0x0e8a76bf7295d9316704fde7f953eced612daa9ca7a70322248eeb8a7f508656":"Transfer",??????"0x4947b4f075f8e9f89f6364158b3d05a92cd72b7920c44c2150a0d12ba009a7a0":"Convert",??????"0x5f37bb3b9734175b605f6e02700c4b710e5e01622f30d822bcca227d91363d77":"SwapExactETHForTokens",??????"0xdff10159275e064dad2c7c79585d1f3c4fd60b73d843715e0cff1a2292730e99":"RemoteLiquidityETH",??????"0xb8889bbdeb478809c3781ccb1c8a16f9fa90b6844d180818b6e73a16963a5ddc":"SwapExactTokensForETH"????},????"profit":"1.9761631ether"??},??{????"KP3R/WETH":{??????"0xe5a025658cd28a688442a57a9b441980feeed8f5e7892064efc68966eb4253eb":"SwapExactETHForTokens",??????"0xe77e7e9d636c2b733d226693d95d06005ae2b5aa8532957240310225aa73e051":"Approve",??????"0x5ce8451f9f39f2d32ffbd943d38723a8da6fff59ece8f62caa84c4c2a311ede3":"AddLiquidityETH",??????"0x171b741bb7cdcafebdbed1c503eb33babc70c2e2e45b2b55330df3bc6d5c9eda":"Approve",??????"0x0ad658ebab282a26d67da0a97083a41c83d0eb1ab6d19a4adb3676b57fc3851c":"AddLiquidityETH",??????"0x676dd29fade2b93e5ca4b0da9d2b5e4ede86f69d26a6201440e359892360b096":"Transfer",??????"0x3b37a792edbb785b223a2b4f0971834083acd52503e54d00989a365bbc533627":"Convert",??????"0x4df5506fdc7616ff65b4ae3b93360e180c7b6f5e976914c4af04648ad6559817":"SwapExactETHForTokens",??????"0x07e56eaa7935fb341654ac20223b0d32fab006b3f34e372aecf6bce05c3f903f":"RemoveLiquidityETH",??????"0x8f4d9d676e9a12d07dcd0c8225e207df48f8cb575cdaa6d81c4b7124c3500510":"Approve",??????"0xac3c837c249fb68ceebd896a72e1e4e8cf355caf3f5fcd0bdc7df7c101ea0596":"SwapExactTokensForETH"????},????"profit":"1.8226875ether"??},??{????"YFI/WETH":{??????"0x1b0eb70bc4d2407745df416acf6e2c312d25ee63c7e8e1291545d66e23fbf704":"PreAttack",??????"0x8f6caabd4ecfad30793db76f60a7e28832a18e2bcf006c0ee3652063c7386778":"Convert",??????"0xe6d28052b55ab520a211daebbc67ee3aece6ae356044e9352fc82910214a038a":"Swap"????},????"profit":"-0.031382ether"??},??{????"AXS/WETH":{??????"0x375f5befeb1af976ebb09cf5539b3a3b9746b87153cfa96ba862deb8828970f1":"PreAttack",??????"0xed8508a18c347c3829024f7acb94056a78cc63152e2246ebd42b59cd86d0c8f9":"Convert",??????"0xd08eb264e39cd5dca8edb3684dfd36afb905aea9c47a43110b6c5c45bdb2f7d1":"Swap"????},????"profit":"1.349482ether"??},??{????"CRD/WETH":{??????"0xc6c86de784359a3813b31b4be5806a23f82fdd8d5cd9bd3a7379d33a413eb920":"PreAttack",??????"0x7d1b36019fb287867419dffb281b5ad73b37d8dc21abca47f7b618875842ef0a":"Convert",??????"0x8c14595b205cd04d1e5062a3efe47d3e4dae946eabe744e2d8350d6ba951495a":"Swap"????},????"profit":"1.325357ether"??},??{????"USDC/WETH":"Failed"??},??{????"COVER/WETH":"Failed"??},??{????"YAX/WETH":{??????"0x063bc5df97c0ec87d6c309b54fbc4e3ed13b22f5a115fb1170015e4e9d23cd3d":"PreAttack",??????"0x9537551d0db7ed6ae372c050c73cae1272f4d7e7847ea908d6e4d440809a871f":"Convert",??????"0x9f6bdf1c9065f5f5e5c71f32058093b7ac06e140c3a33db2f21cc8a5ff8a5d21":"SwapExactETHforTokens",??????"0x9281c35277ea6594924600d70b73077a4307973c540edb5b4ed534c7e25f2423":"Approve",??????"0xe2f682d8b4801061d504025f11b3032648a3b94019396f7b12749b162f8404cf":"RemoteLiquidityETH",??????"0xf6ea6c9eb92ca9aed70e8b4b03a6e5565a3a13df71a0aa527fa55607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BTC突破23700美元關口 日內漲幅為1.62%:火幣全球站數據顯示，BTC短線上漲，突破23700美元關口，現報23719.0美元，日內漲幅達到1.62%，行情波動較大，請做好風險控制。[2020/12/23 16:18:17]

后續攻擊者又嘗試攻擊Sushiswap的其他相關仿盤項目，如LuaSwap：

https://etherscan.io/tx/0xeacfed6fb18563c18b9af5cb0d3a5b13e97cf02026ef9a4cb625cc33580d02a7

但可能獲利不多，只成功幾筆就不了了之了

2.2本次事件后續結果：

在**#11351530**塊，Sushi的管理員向攻擊者喊話：

可以看到，好像有些延遲，攻擊者的攻擊依然持續了一段時間：

最后一條Convert中：

SushiMaker地址從0x6684977bBED67變成了0x280ac711bb99d：

Old：0x6684977bBED67e101BB80Fc07fCcfba655c0a64F??functionconvert(addresstoken0,addresstoken1)public{????//Atleastwetrytomakefront-runninghardertodo.????//限制只能EOA來調用該函數????require(msg.sender==tx.origin,"donotconvertfromcontract");????//獲取相應SLPtoken合約的地址????IUniswapV2Pairpair=IUniswapV2Pair(factory.getPair(token0,token1));????//將SushiMaker中存有的全部SLP，轉給交易池????pair.transfer(address(pair),pair.balanceOf(address(this)));????//Burn掉這些SLP換成兩種token????pair.burn(address(this));????//分別將兩種token找到相應的和wETH的交易對，全部轉換為wETH????uint256wethAmount=_toWETH(token0)_toWETH(token1);????//將轉換的到的全部wETH找wETH/SUSHI交易對換成SUSHI_toSUSHI(wethAmount);??}??function_toETH(addresstoken){????...????uintamountIn=IERC20(token).balanceOf(address(this));??}New：0x280ac711bb99dE7C73FB70fb6DE29846D5e4207F??functionconvert(addresstoken0,addresstoken1)public{????//Atleastwetrytomakefront-runninghardertodo.????require(msg.sender==tx.origin,"donotconvertfromcontract");????IUniswapV2Pairpair=IUniswapV2Pair(factory.getPair(token0,token1));????pair.transfer(address(pair),pair.balanceOf(address(this)));????(uintamount0,uintamount1)=pair.burn(address(this));????uint256wethAmount=_toWETH(token0,amount0)_toWETH(token1,amount1);_toSUSHI(wethAmount);??}??function_toETH(addresstoken,uintamountIn){????...??}

可以看到區別在于：代碼第26行_toWETH限制了amount，這樣修改以后就不會將SushiMaker中存的全部SLP都去池中換成wETH，而只是換取burn出的一部分

但是這樣問題就解決了嗎？其實還沒有，時隔兩個月，同樣的地方，Sushiswap又中槍了見：amenda：SushiSwap攻擊事件(2021年1月27號)分析(https://zhuanlan.zhihu.com/p/372058217)

0x3.參考

以小博大，簡述SushiSwap攻擊事件始末：https://www.chainnews.com/zh-hant/articles/726256718885.htm

Astokenpricerisesandreputationmends,Sushiswapfoilsmidnightexploit:?https://cointelegraph.com/news/as-token-price-rises-and-reputation-mends-sushiswap-foils-midnight-exploit

DASH突破76美元關口 日內漲幅為4.58%:火幣全球站數據顯示，DASH短線上漲，突破76美元關口，現報76.02美元，日內漲幅達到4.58%，行情波動較大，請做好風險控制。[2020/10/22]

AnevolutionofUniswapwithSUSHItokenomics：https://sushichef.medium.com/the-sushiswap-project-dd6eb80c6ba2

一文看懂Uniswap和Sushiswap：https://zhuanlan.zhihu.com/p/226085593

sokdecentralizedexchanges(dex)withautomatedmarketmaker(amm)protocols:?https://arxiv.org/abs/2103.12732

AttackingtheDeFiEcosystemwithFlashLoansforFunandProfit:?https://arxiv.org/abs/2003.03810

https://www.blocksecteam.com/

BTC在1小時內跌幅超過1.00%:據火幣全球站數據顯示，BTC/USDT在1小時內出現劇烈波動，跌超1.00%，達到-1.05%。當前報價為5911.45美元，行情波動較大，請注意風險控制。[2020/3/30]

行情丨ETH在1小時內漲幅超過3.00%:據火幣全球站數據顯示，ETH/USDT在1小時內出現劇烈波動，漲超3.00%，達到3.36%。當前報價為 255.52 美元，行情波動較大，請注意風險控制。[2020/2/17]

Tags：ETHWETWETHSWAPCRETH2價格WETAweth幣等于多少人民幣IX Swap

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