Emerging “Sandwich Attack” Exploits Blockchain Transactions: A Closer Look

Blockchain technology has enabled secure, peer-to-peer financial transactions through its decentralized nature. However, with every innovation comes challenges. Recently, an alarming attack vector, termed the “Sandwich Attack“, has surfaced, drawing significant attention from the crypto community.

Understanding the Sandwich Attack

A “sandwich attack” pertains to a situation where a malevolent actor “sandwiches” a user’s transaction between their own two strategically placed transactions. This maneuver can result in potential financial losses for the unsuspecting victim while allowing the attacker to amass profits.

The primary mechanics of this attack exploit the blockchain’s mempool. For the uninitiated, the mempool is essentially a waiting room for transactions yet to be confirmed on the blockchain. Here, transactions wait for miners to pick them up and add them to the next block. Certain parameters, like transaction fees, determine the sequence of their processing.

Why Does This Attack Exist?

The feasibility of the sandwich attack is rooted in how transaction confirmations work, particularly when a user, either out of urgency or lack of understanding, sets an unusually high slippage. High slippage indicates the user’s willingness to tolerate a higher price deviation from the market rate. This, when combined with the dynamics of the mempool, becomes fertile ground for attackers to exploit by manipulating the order of transactions.

Mechanics of the Exploitation

To execute a sandwich attack, the attacker employs a two-step approach:

  1. Front-running the Victim’s Transaction: The attacker observes a potentially profitable transaction in the mempool and swiftly sends their own transaction with a higher gas fee and miner tip. This ensures that the attacker’s first transaction will be accepted before the victim’s due to its higher fee. Miners prioritize transactions with higher fees as it’s more profitable for them.
  2. Sealing the Deal: After the victim’s transaction is accepted, the attacker sends a second transaction. This transaction typically has an equal or lower gas fee, ensuring its acceptance after the victim’s transaction. As a result, the victim’s transaction ends up sandwiched between the attacker’s two transactions.

The Attacker’s Gain

So, how does the attacker turn this sandwich into profit?

Once the victim’s transaction is strategically sandwiched, the attacker can buy an asset from the victim at a value significantly lower than its current market value. Following this, the attacker can immediately sell the asset at the market rate. The resulting profit for the attacker is the difference between the sale revenue and the gas fees they incurred during the attack.


The emergence of the sandwich attack is a stark reminder that as blockchain and cryptocurrency technologies evolve, they also open doors to sophisticated vulnerabilities. Users are advised to remain vigilant, ensure they understand the intricacies of transaction fees, and always be cautious when setting high slippage rates. As the crypto ecosystem works towards mitigating such threats, it underscores the importance of continuous research and adaptive measures to shield users from potential pitfalls.

Crypto products and NFTs are unregulated and can be highly risky. There may be no regulatory recourse for any loss from such transactions. Crypto is not a legal tender and is subject to market risks. Readers are advised to seek expert advice and read offer document(s) along with related important literature on the subject carefully before making any kind of investment whatsoever. Crypto market predictions are speculative and any investment made shall be at the sole cost and risk of the readers.