Solana is a young blockchain, and having a complete picture of what is happening on-chain is a difficult task — especially due to the high number of transactions daily processed. The current number of TPS is around 2,000, meaning that we need to deal with ~ 10⁸ transactions per day, see Fig. 1.1.
When processing transactions, we have to deal with the impossibility of a-priori knowing its status before querying information from an RPC node. This means that we are forced to process both successful and failed transactions. The failed transactions, most of which come from spamming bots that are trying to make a profit (e.g. NTF, arbitrage, etc.), constitutes ~ 20% of the successful ones. The situation slightly improves if we consider only program activity. By only considering what happens on Decentralized Exchanges (DEXs), we are talking about 4x10⁷ transactions per day, see Fig. 1.2. This makes it clear that a big effort is required to assess which type of Maximum Extractable Value (MEV) attack is taking place and who is taking advantage of it, even because tools like Flashbots do not exist on Solana.
In what follows, we are going to estimate what happened on-chain considering only ~5 h of transactions on Orca DEX, from 11:31:41 to 16:34:19 on 2022–03–14. This simplification is done to get familiarity with data, extrapolating as much information as we can to extend towards a future analysis by employing a wider range of transactions. It is worth mentioning that Orca DEX is not the program with the highest number of processed instructions, which indicates that a more careful analysis is needed to look also into other DEX — this is left for future study.
The aim of this preliminary analysis is to gain familiarity with the information contained in usual swap transactions. One of our first attempts is to extrapolate if sandwich attacks are happening, and if so, with which frequency. In Section 2, we are going to look at the anatomy of a swap transaction, focussing on the type of sandwich swap in section 2.1. Section 2.2 is devoted to the description of “actors” that can make a sandwich attack. In Section 3, we describe the dataset employed, leaving the description of the results in Section 4. Conclusions are drawn in Section 5.
On Solana, transactions are made by one or more instructions. Each instruction specifies the program that executes them, the accounts involved in the transaction, and a data byte array that is passed to the program. It is the program’s task to interpret the data array and operate on the accounts specified by the instructions. Once a program starts to operate, it can return only two possible outcomes: success or failure. It is worth noticing that an error return causes the entire transaction to fail immediately. For more details about the general anatomy of the transaction see the Solana documentation.
To decode each of the instructions we need to know how the specific program is written. We know that Orca is a Token Swap Program, thus we have all the ingredients needed to process data. Precisely, taking a look at the token swap instruction, we can immediately see that a generic swap takes as input the amount of token that the user wants to swap, and the minimum amount of token in output needed to avoid excessive slippage, see Fig. 2.1.
The minimum amount of tokens in output is related to the actual number of tokens in output by the slippage S, i.e.
from which
Thus, we can extract the token in input and the minimum token in output from the data byte array passed to the program, and the actual token in output by looking at the instructions contained in the transaction.
By computing the corresponding slippage defined in Eq. (2.2) we obtain the histogram in Fig. 2.2. From this picture, we can extrapolate different information. The first one is, without doubt, the distribution of transactions around the default value of slippage on Orca, i.e. 0.1%, 0.5% and 1%. This makes complete sense since the “common-user” is prone to use default values, without spending time in customization. The second one is the preference of users to select the lowest value for the slippage. The last one concerns the shape of the tails around the default values. A more detailed analysis is needed here since it is not an easy task to have access to what actually is contained inside them. The shape surely depends on the bid/ask scatter, which is a pure consequence of the market dynamic. The tails may also contain users that select a different slippage with respect to the default values. However, one thing is assured: this histogram contains swaps from which the slippage can yet be extracted. As we will see, from this we can extrapolate an estimate of the annualized revenue due to sandwich attacks.
The goal of this report is to search for hints of sandwich swaps happening on Orca DEX. All findings will be used for future research, thus we think it is useful to define what we refer to as sandwich swaps and how can someone take advantage of them.
Let’s start with its basic definition. Let’s assume a user (let’s say Alice) wants to buy a token X on a DEX that uses an automated market maker (AMM) model. Let’s now assume that an adversary sees Alice’s transaction (let’s say Bob) and can create two of its own transactions which it inserts before and after Alice’s transaction (sandwiching it). In this configuration, Bob buys the same token X, which pushes up the price for Alice’s transaction, and then the third transaction is the adversary’s transaction to sell token X (now at a higher price) at a profit, see Fig. 2.3. This mechanism works until the price at which Alice buys X remain sbelow the value X･(1+S), where S represents the slippage set by Alice when she sends the swap transaction to the DEX.
Since Bob needs to increase the value of the token X inside the pool where Alice is performing the swap, it is evident that the core swaps inserted by Bob should live on the same pool employed by Alice.
From the example above, it may happen that Bob does not have the capital needed to significantly change the price of X inside the pool. Suppose that the pool under scrutiny regards the pair X/Y and that the AMM implements a constant product curve. In the math formula we have:
where k is the curve invariant. If we set the number of tokens Y in the pool equal to 1,000,000 and the number of tokens X equal to 5,000,000 and assuming that Alice wants to swap 1,000 token Y, we have that the amount of token X in output is:
It is worth noting that here we are not considering the fee that is usually paid by the user. If Alice set a slippage of 5%, this means that the transaction will be executed until the output remains above 4'745.25. This means if Bob is trying to take this 5%, he will need an initial capital of 26,000 token Y.
Sometimes this capital may be inaccessible, allowing Bob to only take a portion of the 5% slippage. For example, let’s consider the Orca pool SOL/USDC, with a total value locked (TVL) of $108,982,050.84 at the time of writing. This pool implements a constant product curve, which allows us to use Eqs. (2.3) and (2.4) to simulate a sandwich attack. Fig. 2.4 shows the result of this calculation.
It is clear that the initial capital to invest may not be accessible to everyone. Further, it is important to clarify that the result is swap-amount independent. Indeed, for each amount swapped by Alice, the swap made by Bob is the one that “moves” the prices of the initial tokens inside the pool. The scenario is instead TVL dependent. If we repeat the same simulation for the Orca pool ETH/USDC, with a TVL of $2,765,189.76, the initial capital needed to extract a higher percentage of the slippage of Alice drastically decreases, see Fig. 2.5.
From the example above, let’s consider the case in which Bob has an initial capital of 2,000 token Y. If he is able to buy the token Y before Alice’s transaction, Alice will obtain an output of 4,975.09 token X, which is only 0.4% lower than the original amount defined in Eq. (2.4).
At this point, Bob has another possibility. He can try to order transactions that are buying the same token X after its transaction, but immediately before Alice’s swap. In this way, he can use the capital of other users to take advantage of Alice’s slippage, even if Bob’s initial capital is not enough to do so, see Fig. 2.6. This of course results in a more elaborate attack, but likely to happen if Bob has access to the order book.
It is not an easy task to spot the actors behind a sandwich attack on Solana. In principle, the only profitable attackers are the leaders. This is because there isn’t a mempool, and the only ones that know the exact details of the transactions are the validators that are in charge of writing a block. In this case, it may be easier to spot hints of a sandwich attack. Indeed, if a leader orders the swap transactions to perform a sandwich, it should include all of them in the same block to prevent an unsuccessful sandwich.
The immediately following suspect is the RPC service that the DAPP is using. This is because the RPC service is the first to receive the transaction over HTTP, since it is its role to look up the current leader’s info using the leader schedule and send it to the leader’s Transaction Processing Unit (TPU). In this case, it would be much more difficult to spot hints of sandwiching happening since in principle the swap transactions involved can be far from each other. The only hook we can use to catch the culprit is to spot surrounding transactions made by the same user, which will be related to the RPC. This is a consequence of the lower price fee on Solana, which raises the likelihood that a sandwich attack can happen by chance spamming transactions in a specific pool. This last one is clearly the riskiest since there is no certainty that the sequence of transactions is included in the exact order in which the attacker originally planned it.
Before entering the details of the analysis, it is worth mentioning that, standing on what is reported on Solana Beach, we have a total of 1,696 active validators. Our sample contains 922 of them, i.e. 54.37% of the total validator population. The table below shows the validator that appears as the leader in the time window we are considering. Given the likelihood-by-stake for a validator to be selected as a leader, we retain fair to assume that our sample is a good representation of what’s happening on Orca. Indeed, if a validator is running a modified version of the vote account program to perform sandwich swap, the rate of its success will be related to the amount of staked tokens, not only by actual MEV opportunities. Further, modifying the validator is not an easy task, thus smaller validators will not have the resources to do that. Since we have all the 21 validators with a supermajority plus a good portion of the others (i.e. we are considering half of the current number of active validators), if such a validator exists, its behaviour is easily spotted in our sample. However, it is worth mentioning that a complete overview of the network requires the scrutiny of all validators, without making assumptions of that kind. Such achievement is behind the scope of this report, which aims primarily to explore which type of sandwich can be done and how to spot them.
Having clarified this aspect, we firstly classify the types of swaps that are performed on the Orca DEX. The table below shows the accounts that are performing more than two transactions. It is immediately visible that most of the transactions are done by only 2 accounts over 78 involved.
As explained in Section 1, we are considering 5H of transactions on Orca DEX, from 11:31:41 to 16:34:19 on 2022–03–14. This sample contains a total of 12,106 swaps, with pool distribution in Fig. 3.1.
By deep-diving into the swap, we can see that most of the transactions in the 1SOL/SOL [aq] and 1SOL/USDC [aq] are done by only two accounts, see Fig. 3.2. Here [aq] stands for Aquafarm, i.e. an Orca’s yield farming program. We can also see the presence of some aggregate swaps in the SOL/USDC [aq] and ORCA/USDC [aq] pools.
We started searching for the presence of leaders performing sandwich swaps. As we described in Section 2.1, in general, a swap can happen in two ways. For both of them, if such a type of surrounding is done by a leader, we should see the transactions under scrutiny included in the same block. This is because, if a leader wants to make a profit, the best strategy is to avoid market fluctuations. Further, if the attacker orders the transactions without completing the surrounding, the possibility that another leader reorders transactions cancelling the effect of what was done by the attacker is not negligible.
By looking at the slots containing more than 3 swaps in the same pool, we ended up with 6 slots of that kind, out of 7479. Deep diving into these transactions, we found that there is no trace of a sandwich attack done within the same block (and so, from a specific leader). Indeed, each of the employed transactions is done by a different user, marking no evidence of surrounding swaps done to perform a sandwich attack. The only suspicious series of transactions is included in block # 124899704. We checked that the involved accounts are interacting with the program MEV1HDn99aybER3U3oa9MySSXqoEZNDEQ4miAimTjaW, which seems to be an aggregator for arbitrage opportunities.
As mentioned in Section 2.2, validators are not the only possible actors. Thus, to complete the analysis we also searched for general surrounding transactions, without constraining them to be included in the same block. We find that only 1% of the total swaps are surrounded, but again without strong evidence of actual sandwich attacks (see Fig. 4.1 for the percentage distribution). Indeed, by looking at those transactions it comes out that the amount of token exchanged is too low to be a sandwich attack (see Sec. 2).
Before ending this section, it is worth mentioning that if we extrapolate the annual revenue that a leader obtains by taking 50% of the available slippage for swaps with a slippage greater than 1%, we are talking about an amount of ~ 240,000.00 USD (assuming that the attacker is within the list of 21 validators with supermajority), see Fig. 4.2. Of course, this is not a real estimate since it is an extrapolation from only 5h of transactions, thus we need to stress that the actual revenue can be different. Further, this is not an easily accessible amount due to what we showcased in Sec. 2. However, the amount in revenue clearly paves the way for a new type of protection that validators should offer to users, especially if we take into account that Orca is not the DEX with the highest amount of processed swaps. Since at the moment there is no evidence that swaps are sandwiched, we will take no action in this direction. Instead, we will continue monitoring different DEXs by taking snapshots in different timeframes informing our users if a sandwich attack is spotted on Solana.
In this report, we define two types of sandwich attacks that may happen on a given DEX. We further describe who are the possible actors that can perform such a type of attack on Solana and how to spot them. We analyzed data from ~5 h of transactions on Orca DEX, from 11:31:41 to 16:34:19 on 2022–03–14 (that is, 12,106 swaps). Despite the cutting of the number of transactions employed, we argued why we believe this sample could fairly be a “good” representation of the entire population.
Our findings show no evidence that sandwich attacks are happening on Solana by considering two possibilities. The former is that a validator is running a modified version “trained” to perform a sandwich attack on Orca. The latter is that an RPC is trying to submit surrounding transactions. We discovered that only 1% of transactions are actually surrounded by the same user, but none of them is included in the same block — excluding the possibility that a leader is taking advantage of the slippage. By deep-diving into this, we discover that the amount exchanged by these transactions results are too low for capital to be invested to exploit the slippage and submit a profitable sandwich attack.
We also show how the capital needed to make sandwich attacks profitable may not be accessible to everyone, narrowing the circle of possible actors.
