Prevention of race conditions in the system
import express from 'express';
const app = express();
let data = '';
app.get('/api/data', (req, res) => {
res.send(data);
});
app.post('/api/data', (req, res) => {
const newData = req.body.data;
data = newData;
res.send('Data updated successfully');
});
app.listen(3000, () => {
console.log('Server started on port 3000');
});
The vulnerability in this code is a race condition.
A race condition occurs when multiple threads or processes access shared data concurrently, and the result of the execution depends on the order in which the threads/processes are scheduled. In this case, the vulnerability arises because the
data variable is accessed and modified by multiple requests simultaneously.
In the code, the
data variable is a shared resource that can be accessed and modified by both the GET and POST routes. The GET route returns the current value of
data, while the POST route updates the value of
data based on the request body.
If multiple requests are made to the POST route simultaneously, there is a possibility that the value of
data can be overwritten or modified incorrectly. For example, if two requests are made to update
data at the same time, the value set by one request may be overwritten by the other request, leading to unexpected behavior.
This vulnerability can have several impacts. An attacker could potentially exploit this race condition to overwrite, delete, or read arbitrary files from the system. Additionally, it can cause unexpected behavior in the application, leading to data corruption or inconsistent states.
To mitigate this vulnerability, it is recommended to ensure that the verification and use of inputs are performed atomically or in a synchronized manner. This can be achieved by using locks, mutexes, or other synchronization mechanisms to ensure that only one request can modify the
data variable at a time.
import express from 'express';
import { Mutex } from 'async-mutex';
const app = express();
const mutex = new Mutex();
let data = '';
app.get('/api/data', (req, res) => {
mutex.acquire().then((release) => {
try {
res.send(data);
} finally {
release();
}
});
});
app.post('/api/data', (req, res) => {
const newData = req.body.data;
mutex.acquire().then((release) => {
try {
data = newData;
res.send('Data updated successfully');
} finally {
release();
}
});
});
app.listen(3000, () => {
console.log('Server started on port 3000');
});
The fixed code addresses the race condition vulnerability by implementing a mutual exclusion mechanism using the
async-mutex library.
First, the code imports the necessary dependencies, including the
express framework and the
Mutex class from the
async-mutex library.
Then, an instance of the
express application is created, and a new mutex object is instantiated using the
Mutex class.
A global variable
data is declared to store the data that will be accessed and modified by the routes.
The code defines two routes: a GET route at '/api/data' and a POST route at '/api/data'.
In the GET route, the mutex is acquired using the
acquire() method, which returns a promise. Once the mutex is acquired, the callback function is executed. Inside the callback, the response is sent with the current value of
data. Finally, the mutex is released using the
release() method.
In the POST route, the request body is extracted to get the new data. Similar to the GET route, the mutex is acquired, and the callback function is executed. Inside the callback, the
data variable is updated with the new value, and a success message is sent in the response. Finally, the mutex is released.
By using the mutex, only one request can acquire the lock at a time, ensuring that the critical sections of code (accessing and modifying
data) are executed atomically. This prevents multiple requests from interfering with each other and avoids the race condition vulnerability.
The application is then started and listens on port 3000, with a log message indicating that the server has started.