---
# System prepended metadata

title: MEV

---

# MEV bot audit

### 1. Private Key Exposure

#### **Code Segment:**

``` javascript
const { walletAddress, walletPrivate, ... } = data;
plan.private = walletPrivate;
```

#### **Vulnerability:**
When dealing with cryptographic systems, especially those involving financial operations like in blockchain, private keys are akin to the most sensitive of passwords. Possession of a private key allows the holder to authorize transactions, essentially granting full control over the associated funds or assets.

In the provided code, the private key is being received from a client and set to a variable on the server side. This presents a serious security risk for a few reasons:
#### Risks:
1. Transmission Risk: If the private key is transmitted over the internet without secure encryption (like HTTPS), it can be intercepted by attackers.
2. Storage Risk: Storing the private key in server memory or, worse, in persistent storage exposes it to anyone who can access that memory or storage. This includes potentially malicious server administrators, attackers who gain server access, or even other software running on the same server.
3. Usage Risk: Any operation done with this private key on the server-side can potentially be observed, logged, or manipulated.

#### **Recommendations:**
1. Avoid Transmission:
Do not send private keys over the network. Instead, only send public information and perform sensitive operations client-side.
For instance, if you need to sign a transaction, send the transaction details to the client, sign it there using the private key, and then send back only the signed transaction.
2. Client-Side Wallets:
Use client-side wallet solutions. There are many libraries and tools available, like MetaMask or WalletConnect, that allow web applications to request signatures or other private key operations without the key ever leaving the user's device.
3. Server-Side Encryption:
If there's an absolute necessity to handle private keys server-side (which is a rare case and usually not recommended), ensure they're encrypted in memory and never logged or written to persistent storage in plaintext. Only decrypt them at the exact moment of use and immediately discard the decrypted key.
4. Detailed Logging & Monitoring:
While not a solution to the exposure problem, having detailed logging and monitoring can help detect and respond to unauthorized access or suspicious activities. However, be careful not to log sensitive information.

#### **Code Improvements:**
Given the above, a safer pattern when you need a transaction to be made would look something like this:
1. Server sends transaction details to Client.
2. Client signs the transaction with the private key (locally, without exposing it).
3. Client sends the signed transaction back to the Server.
4. Server broadcasts the signed transaction to the network.

This way, the server never sees or handles the private key directly, reducing the risk significantly.

In conclusion, the handling and storage of private keys are critical aspects of any cryptographic system. Proper care and security considerations need to be taken into account to ensure that these keys remain confidential and aren't exposed to potential attackers.

### 2. Lack of Input Validation

#### **Code Segment:**
```javascript
socket.on("start-get-price-data", async (data) => {
    data = JSON.parse(data);
    const { tokenAddress, tradeAmount } = data;
    ...
```
#### **Vulnerability:**
Input validation is a foundational security principle, and it's paramount when building applications that deal with the internet or user-generated data. The provided code accepts user input from a client through a socket event and immediately processes that data without checking if it's in the expected format or if it contains malicious content.

#### Risks 
Here are potential risks in the given code:

1. Type Consistency: There's no assurance that tokenAddress is a string representing a valid Ethereum address or that tradeAmount is a number or a numeric string.
2. Malformed Data: Since the data isn't validated, malicious or malformed data might crash the server or cause unexpected behavior.
3. Reentrancy Attacks: In the context of Ethereum and smart contracts, without proper validation or sequencing of events, reentrancy attacks could occur, though they're more directly related to the contract's code.

#### **Recommendations:**
1. Schema Validation:
Use libraries like Joi or express-validator to define the shape and content of the expected data. Check the type, format, and any other necessary attributes of the data.
Example:
```javascript
const Joi = require('joi');

const schema = Joi.object({
    tokenAddress: Joi.string().alphanum().length(42).required(),
    tradeAmount: Joi.number().positive().required()
});

const validationResult = schema.validate(data);
if (validationResult.error) {
    console.error("Invalid input data:", validationResult.error.details);
    return;
}
```
2. Boundary Checks:
Ensure that numeric values like tradeAmount are within expected boundaries to prevent overflow, underflow, or economically irrational operations.
3. Sanitize Inputs:
Before using the provided data in any operations, especially database operations or third-party calls, sanitize the data to protect against SQL injection, command injection, or other similar vulnerabilities.
4. Handle Unexpected Data Gracefully:
If data is found to be inconsistent or malicious, handle it gracefully. Log the attempt, alert as needed, and don't crash the application.
#### Code Improvements:
Integrate a validation step right after parsing the received data:
```javascript
const Joi = require('joi');

socket.on("start-get-price-data", async (data) => {
    data = JSON.parse(data);
    
    // Validation
    const schema = Joi.object({
        tokenAddress: Joi.string().alphanum().length(42).required(),
        tradeAmount: Joi.number().positive().required()
    });
    const validationResult = schema.validate(data);
    if (validationResult.error) {
        console.error("Invalid input data:", validationResult.error.details);
        return;
    }

    const { tokenAddress, tradeAmount } = data;
    ...
});
return;
}
```
By following the above guidelines, the server will be better equipped to handle and defend against malicious or unexpected data inputs. This not only ensures the safety and stability of the system but also contributes to a more reliable user experience.

### 3. Insecure Handling of Private Data
#### **Code Segment:**
```javascript
socket.on("start-auto-trading", async (params) => {
    let data = JSON.parse(params);
    const { walletAddress, walletPrivate, tokenAddress, tradeAmount, gasLimit } = data;

    plan.public = walletAddress;
    plan.private = walletPrivate;
    ...
});
```
#### **Vulnerability:**
The code directly accepts and processes the private key (walletPrivate) of a user's Ethereum wallet. Handling, storing, or transmitting private keys insecurely can lead to the compromise of these keys and the assets they control. It exposes users to severe risks, including theft of funds.

#### **Risks:**
1. Exposure of Sensitive Data: Storing private keys in memory, especially if the variable or data structure is global or widely accessible, could allow unauthorized access if there's any form of code injection vulnerability elsewhere in the system.
2. Data Transmission Risks: If the private key is being sent over the internet, there's a risk of interception unless secured by strong encryption (like TLS).
3. Long-term Storage Concerns: If this key is ever stored in a database or file, it's at risk if there are any vulnerabilities in the storage mechanism or if the database/filesystem gets compromised.

#### **Recommendations:**
1. Avoid Direct Handling:
Instead of directly processing private keys, use OAuth or token-based authentication mechanisms to authenticate and authorize users.
In the context of Ethereum, consider utilizing wallet services that enable transaction signing on the client-side, such as MetaMask.
2. Encrypt Sensitive Data:
If there's an absolute need to handle private keys, ensure they're encrypted in transit and at rest.
In transit: Use HTTPS (TLS) for any data transmissions.
At rest: Use strong symmetric encryption algorithms.
3. Restrict Access:
Limit access to sensitive data both programmatically (in the application code) and physically (on the server or database).
Ensure proper role-based access controls if multiple users or roles are interacting with the system.

4. Monitor and Audit:
Keep logs of access to sensitive data and regularly audit these logs for suspicious activity.

#### **Code Improvements:**
Given the vulnerabilities and the recommended measures, here's a revised strategy:

1. Client-Side Signing:
Instead of sending the private key to the server, let the client (user's browser or application) sign a transaction or message. Then, send the signed transaction to the server for broadcasting.
```javascript
// On the client-side (Pseudo-code)
const tx = { /* ... transaction details ... */ };
const signedTx = userWallet.signTransaction(tx);
socket.emit('broadcast-transaction', signedTx);

```
```javascript
// On the server-side
socket.on('broadcast-transaction', async (signedTx) => {
    try {
        const txReceipt = await ethProvider.sendTransaction(signedTx);
        console.log('Transaction broadcasted:', txReceipt);
    } catch (error) {
        console.error('Error broadcasting transaction:', error);
    }
});
```
2. Secure Communication:
Ensure that the connection between the client and the server is secured using HTTPS (TLS). This is especially crucial when handling sensitive data, including signed transactions.

3. Avoid Storing Private Keys:
If for some reason you still need to work with private keys, never store them in long-term storage. If temporary storage is required, ensure encryption and proper access controls.

By adopting these measures, you can enhance the security of the system, protect user data, and establish trust with your users. Remember, in the world of cryptocurrencies and blockchain, once assets are stolen due to compromised keys, it's almost impossible to recover them.

### 4. Lack of Validation and Sanitization
#### **Code Segment:**
```javascript
socket.on("start-get-price-data", async (data) => {
    data = JSON.parse(data);
    const { tokenAddress, tradeAmount } = data;
    ...
});
```

#### **Vulnerability:**
The data being received from the socket is being directly parsed without any prior validation or sanitization. This makes the application vulnerable to various types of injection attacks if malicious data is sent.

#### **Risks:**
1. JSON Injection: An attacker might send malicious JSON payloads that, when parsed, can change the structure or content of the data object, leading to unexpected behavior or logic flaws in the subsequent code.
2. Unintended Behaviors: Without proper validation, it's possible to pass in non-expected values for tokenAddress and tradeAmount which could lead to unpredictable results in the subsequent logic.
3. Resource Exhaustion: An attacker might send an extremely large payload, causing resource exhaustion and possibly crashing the server or service.

#### **Recommendations:**
1. Validation:
Validate the structure of the incoming JSON data to ensure it contains only the expected fields.
For Ethereum addresses like tokenAddress, ensure they match the standard Ethereum address format.
For numeric values like tradeAmount, ensure they're valid numbers and within expected ranges.
2. Sanitization:
Sanitize all incoming data to remove or neutralize potentially malicious content.
3. Error Handling:
Implement robust error handling to manage incorrect or malicious data gracefully without crashing the service.
4. Size Limitation:
Implement size limits for incoming data to prevent resource exhaustion attacks.

#### **Code Improvements:**
Given the vulnerabilities and the recommended measures, here's a revised approach to handle the data:
```javascript
socket.on("start-get-price-data", async (rawData) => {
    if (typeof rawData !== 'string' || rawData.length > MAX_DATA_SIZE) {
        console.error("Invalid data received.");
        return;
    }

    let data;
    try {
        data = JSON.parse(rawData);
    } catch (e) {
        console.error("Error parsing JSON:", e);
        return;
    }

    if (!data.tokenAddress || !data.tradeAmount) {
        console.error("Required fields missing.");
        return;
    }

    // Validate Ethereum address format
    if (!ethers.utils.isAddress(data.tokenAddress)) {
        console.error("Invalid Ethereum address.");
        return;
    }

    // Validate tradeAmount as a positive number
    const tradeAmount = parseFloat(data.tradeAmount);
    if (isNaN(tradeAmount) || tradeAmount <= 0) {
        console.error("Invalid trade amount.");
        return;
    }

    // Continue with the rest of the logic...
    ...
});
```
In this improved code:

* We first check if the incoming data is a string and doesn't exceed a predefined MAX_DATA_SIZE.
* Next, we safely attempt to parse the JSON, handling any potential errors.
* After parsing, we validate the Ethereum address using ethers utility functions.
* Finally, we ensure that tradeAmount is a positive number before continuing.

This approach makes the data handling more robust and secure against potential malicious inputs.

### 5. Potential for DoS Attacks
#### **Code Segment:**
```javascript
socket.on("start-get-price-data", async (data) => {
    ...
    await getPriceMonitor();

    if (intervalGetPriceId !== null) {
        clearInterval(intervalGetPriceId);
    }

    intervalGetPriceId = setInterval(getPriceMonitor, 10000);
    ...
});
```
#### **Vulnerability:**
Every time the `start-get-price-data` event is triggered, the system creates a new interval to repeatedly call `getPriceMonitor()`. The issue arises when this event is triggered repeatedly in quick succession: the system will stack multiple interval processes on top of one another. Although there is a mechanism to clear the previous interval (`clearInterval(intervalGetPriceId);`), this clearing only occurs after the `getPriceMonitor()` function has been awaited, leaving a window where multiple intervals can co-exist.

#### **Risks:**
1. Server Overload: Multiple simultaneous intervals can cause significant strain on the server, especially if each interval involves computationally intensive tasks or calls to external services (e.g., Uniswap).
2. Service Degradation: With the accumulation of interval processes, the quality of service can degrade for other users as the server becomes preoccupied.
3. Potential Financial Cost: If each `getPriceMonitor` call involves a transaction or request to a service that costs money, repeated triggers can escalate costs.

#### **Recommendations:**
1. Limit Frequency: Implement a mechanism to ensure that the "start-get-price-data" event can't be triggered too frequently by the same client. This can be achieved through rate limiting or cooldown periods.
2. Immediate Interval Clearance: Ensure that any existing intervals are cleared immediately upon receiving the "start-get-price-data" event, before any other processing or awaiting.
3. Client Feedback: Inform the client when they're sending requests too frequently, which not only acts as a deterrent but also provides feedback in case of legitimate use.

#### **Code Improvements:**
Here's a modification that immediately clears the previous interval and implements a basic cooldown mechanism:
```javascript
// A mapping of socket IDs to the last time they started price data fetching
const lastFetchTimes = {};

socket.on("start-get-price-data", async (data) => {
    // Immediately clear any existing interval
    if (intervalGetPriceId !== null) {
        clearInterval(intervalGetPriceId);
    }

    // Check for cooldown (e.g., 30 seconds)
    const currentTime = Date.now();
    const lastFetchTime = lastFetchTimes[socket.id] || 0;
    if (currentTime - lastFetchTime < 30000) {
        console.log("Requesting too frequently. Wait for cooldown.");
        socket.emit("error", "You're requesting data too frequently. Please wait.");
        return;
    }
    lastFetchTimes[socket.id] = currentTime;

    // The rest of the logic...
    ...
    intervalGetPriceId = setInterval(getPriceMonitor, 10000);
});
```
This revised approach helps guard against rapid, repeated triggering of the data-fetching event.

### 6. Fixed Gas Limit
#### Code Segment:
```javascript
socket.on("start-auto-trading", async (params) => {
    let data = JSON.parse(params);
    const { walletAddress, walletPrivate, tokenAddress, tradeAmount, gasLimit } = data;

    plan.public = walletAddress;
    plan.private = walletPrivate;
    plan.toToken = tokenAddress;
    plan.autoAmount = tradeAmount;
    plan.autoGasLimit = gasLimit;

    ...
});
```

#### Vulnerability:
The gas limit for transactions is explicitly set via the `gasLimit` variable from the incoming data, which is then assigned to the `plan.autoGasLimit`. Depending on how this `gasLimit` is used in the subsequent transaction signing or sending, this can introduce issues.

#### Risks:
1. Failed Transactions: If a user or attacker sets the `gasLimit` too low, the transaction could fail due to an "Out of Gas" error. This means that, even though no value transfer might happen, the gas used up to the point of failure will still be consumed, resulting in financial loss.
2. Overpaying for Gas: Conversely, if the `gasLimit` is set way too high, and the Ethereum network is not congested, users might end up overpaying for gas unnecessarily.
3. Manipulation: Malicious actors can potentially abuse this to either sabotage the application's transactions or to deliberately force the overpayment of gas fees.

#### **Recommendations:**
1. Dynamic Gas Estimation: Instead of accepting a fixed gas limit from the client, the server should ideally estimate the gas required for the transaction. Ethereum provides functionality for gas estimation which can be used to determine an appropriate gas limit.
2. Range Checks: If for some reason a fixed gas limit input is necessary, implement checks to ensure that the provided gas limit is within reasonable bounds to avoid "Out of Gas" errors or overpayment.
3. Feedback Mechanism: Provide feedback to the client about the estimated gas and potentially allow them to confirm or adjust based on this estimate.

#### Code Improvements:
Here's a modification using the ethers library to estimate gas:
```javascript
socket.on("start-auto-trading", async (params) => {
    let data = JSON.parse(params);
    const { walletAddress, walletPrivate, tokenAddress, tradeAmount, gasLimit } = data;

    // Create a mock transaction to estimate gas
    const mockTransaction = {
        to: tokenAddress,
        value: tradeAmount,
        // ... any other relevant details for the transaction
    };

    try {
        const estimatedGas = await ethProvider.estimateGas(mockTransaction);

        // It's often a good idea to add a buffer, e.g., 20%
        const bufferedGas = estimatedGas.mul(120).div(100);

        plan.autoGasLimit = bufferedGas;

    } catch (error) {
        console.error("Failed to estimate gas:", error);
        return;
    }

    // Proceed with the rest of the logic...
    ...
});
```
This approach attempts to estimate the required gas dynamically, adding a 20% buffer to account for fluctuations in required gas during transaction execution.

### 7. Potential Front-Running
#### Code Segment:
```javascript
socket.on("start-auto-trading", async (params) => {
    ...
    await prepareBot(true);
    io.of("/api/ethers").emit("monitor-message", `Started auto trading`);
    startPlan();
});
```

#### **Vulnerability:**
Front-running is a concern in decentralized finance, especially on public blockchains like Ethereum. Bots can monitor pending transactions and attempt to submit their own transactions with higher gas fees to get them mined faster.

The code provided doesn't directly execute trades, but given the context ("start-auto-trading"), one can infer that trades are executed at some point. If these trades are broadcasted to the Ethereum network without considerations to prevent front-running, malicious actors could take advantage.

#### **Risks:**
1. Financial Loss: Front-running can lead to financial losses. If a malicious actor can deduce what trade the bot is about to make, they can jump ahead, effectively changing the expected outcome of the trade for the original trader.
2. Manipulated Trade Outcome: Even if not for direct financial gain, front-runners can still manipulate the outcome of trades, causing slippage or other undesired results for traders.

#### **Recommendations:**
1. Use Private Transactions (where feasible): Some platforms and solutions allow for private transaction submissions. This can prevent front-runners from viewing the transaction contents until they're confirmed.
2. Gas Price Strategy: Adjust the gas price dynamically based on network congestion. This can make it harder for front-runners to consistently outbid you.
3. Randomized Delays: Introducing a random delay before sending a transaction might make front-running less predictable, though it's not a full-proof method.
4. Look into DEX solutions that mitigate front-running: Some decentralized exchanges have designs that inherently mitigate front-running risks, such as batch auctions.

#### **Code Improvements:**
While the exact transaction submission isn't shown in the provided code, consider these steps for improving transaction submissions to counter front-running:

1. Implement a dynamic gas strategy:
```javascript
async function getOptimalGasPrice() {
    const currentGasPrice = await ethProvider.getGasPrice();
    // Add a multiplier or a fixed amount to the current gas price
    return currentGasPrice.mul(125).div(100);  // e.g., 125% of current price
}
```
2. Use this gas strategy when sending a transaction (assuming a transaction function elsewhere in the code):
```javascript
const gasPrice = await getOptimalGasPrice();
const txResponse = await someContract.someFunction(args, { gasPrice });
```
3. Consider random delays (though not always ideal):
``` javascript
const randomDelay = Math.floor(Math.random() * (maxDelay - minDelay + 1)) + minDelay;
setTimeout(() => {
    // then send the transaction
}, randomDelay);
```
However, it's important to understand that the true mitigation of front-running is complex and can be specific to each application's context and the broader ecosystem in which it operates.

### 8. Potential Reentrancy Attack
#### Code Segment:
``` javascript
socket.on("start-auto-trading", async (params) => {
    ...
    await prepareBot(true);
    io.of("/api/ethers").emit("monitor-message", `Started auto trading`);
    startPlan();
});
```

#### **Vulnerability:**
Reentrancy attacks occur when an external function call is made before the state of a function's variables is settled. In Ethereum, this might mean an external call is made before state changes like balance updates are finalized. Malicious contracts can exploit this by re-entering and executing the function multiple times in a single transaction.

While the exact details of `prepareBot` and `startPlan` functions aren't provided, any external calls or transactions they initiate are potential points of vulnerability.

#### **Risks:**
1. Unintended Execution: Reentrancy can lead to functions being called and executed more times than expected.
2. Financial Loss: If the functions in question are involved in transferring Ether or tokens, reentrancy can lead to loss of funds.
3. State Manipulation: Malicious actors can manipulate contract states in unintended ways.

#### **Recommendations:**
1. Use the Checks-Effects-Interactions Pattern: This design pattern suggests that you should:
* First, check all conditions.
* Then, make any state changes.
* Finally, interact with other contracts.
By following this order, you minimize the potential for a reentrancy attack.
2. Use the reentrancyGuard Modifier: A common pattern to prevent reentrancy is to use a modifier that ensures the function can't be re-entered while it's still being executed.

#### **Code Improvements:**
1. Implementing a `reentrancyGuard`:
``` javascript
let locked = false;

function reentrancyGuard(fn) {
    return async function (...args) {
        if (locked) throw new Error("Reentrant call detected!");
        locked = true;
        try {
            return await fn(...args);
        } finally {
            locked = false;
        }
    };
}
```
2. Apply the guard to functions:
``` javascript
const guardedStartPlan = reentrancyGuard(startPlan);

socket.on("start-auto-trading", async (params) => {
    ...
    await prepareBot(true);  // Assuming this does not make external calls
    io.of("/api/ethers").emit("monitor-message", `Started auto trading`);
    guardedStartPlan();  // Using the guarded version
});
```

However, for smart contracts, it's typical to use Solidity's modifiers. Since the provided code is in JavaScript and the actual contract code isn't shown, it's important to ensure that any functions making external calls in the underlying Solidity code also employ a similar reentrancy guard.

### 9. Error Handling
#### **Vulnerability:**
Several parts of the code have catch blocks that lack robust error handling mechanisms. Instead of taking appropriate action or notifying the user about the specific error, the catch blocks often merely log the error or, in some cases, assign default values.
#### Code Segment 1:
``` javascript
try {
    ...
    uni_buy = await uniswapContract.getAmountsOut(
        ethers.utils.parseUnits(String(tradeAmount), 'ether'),
        [wethaddress, tokenAddress]
    );
    ...
} catch (err) {
    uni_buy = 0;
    console.log(err);
}
```
Here, if there's an error in fetching the buy amount, the uni_buy value defaults to 0 without notifying the user.
#### Code Segment 2:
``` javascript
try {
    let tokenContract = new ethers.Contract(
        tokenAddress,
        erc20abi,
        ethProvider,
    );
    tokenName = await tokenContract.symbol();
    ...
} catch (err) {
    console.error(err);
}
```
In this segment, if there's an error initializing the token contract or fetching the token symbol, the error is merely logged, and the function continues to execute, potentially leading to undefined behavior or more errors down the line.

#### **Risks:**
1. User Experience: Silent failures can lead to user confusion. If something doesn't work as expected, but there's no feedback or alert, users might not know how to proceed or understand what went wrong.
2. Data Integrity: Default values like `uni_buy = 0;` might cause inaccuracies in further processing or calculations.
3. Debugging Difficulty: In the absence of detailed error logs or notifications, debugging issues, especially in a live environment, can be challenging.

#### Recommendations:
1. Detailed Error Messages: While it's vital not to expose sensitive data, having detailed error messages can help users understand the problem and potentially find a solution or report the issue.
2. Notify Users: Instead of silently failing, emit socket messages to notify the user/client about the error, so they can take appropriate action.
3. Graceful Failures: If a critical error occurs, stop further execution of the function and clean up any resources to prevent undefined behavior.

#### Code Improvements:
1. Provide Feedback on Errors:
Add logic to notify the user when an error occurs:
``` javascript
try {
    ...
} catch (err) {
    console.error(err);
    io.of("/api/ethers").emit("error-message", "There was an issue processing your request. Please try again.");
}
```
2. Detailed Error Logging:
Enhance error logging to include contextual information:
``` javascript
catch (err) {
    console.error(`Error fetching token details for address: ${tokenAddress}. Error: ${err.message}`);
}
```
3. Avoid Default Values When Inappropriate:
Rather than assigning potentially misleading default values, handle errors gracefully:
``` javascript
try {
    ...
} catch (err) {
    console.log(err);
    return; // Exit the function or take corrective action instead of using default values.
}
```
By implementing more comprehensive error handling, you not only improve the user experience but also make the system more resilient and easier to maintain.