In today's online world, servers power everything from social media to essential services. Yet they're not always secure. Even with modern technology, many servers face old and new threats. This blog highlights key server vulnerabilities and how to handle them. Dive in to learn about server protection, because knowing the issues is a major step towards fixing them.

1. SQL Injection (SQLi)

• Description:
  SQL Injection is among the most notorious web vulnerabilities. An attacker can use this technique to manipulate SQL queries by inserting malicious SQL code. This manipulation can grant them access to sensitive information, modify database data, or even execute administrative operations on the database.

• Example:
  Imagine a website where users can log in. An attacker might exploit a non-sanitized input field, allowing them to retrieve all usernames and passwords from a database.

const userInput = req.body.username;
const query = `SELECT * FROM users WHERE username = '${userInput}'`;
database.execute(query);

• Solution:
  Avoid raw SQL queries. Instead, use ORM frameworks or prepared statements. By treating user input as data rather than executable code, SQL injections can be mitigated.

const { PrismaClient } = require('@prisma/client');
const prisma = new PrismaClient();

const username = req.body.username;
const user = await prisma.user.findUnique({ where: { username: username } });

---

2. XML External Entity (XXE) Attacks

• Description:
  XXE attacks prey on applications processing XML data. By referencing external entities, attackers can trigger the application to disclose internal files, potentially leading to a myriad of exploits, including remote code execution.

• Example:
  A web application receives XML data. An attacker submits crafted XML data to this service, causing it to fetch or display an internal file's content.

const parse = require('xml-parser');
const xml = req.body.data;
const parsedData = parse(xml);

• Solution:
  Secure XML processing by disabling Document Type Definition (DTD) and external entity processing in XML parsers. Opt for JSON or other less risky data formats when possible.

const parser = require('fast-xml-parser');
const xmlData = req.body.data;

const options = { 
  ... // existing options
  preventEntities: true  // crucial to prevent XXE
};

const jsonData = parser.parse(xmlData, options);

---

3. Broken Authentication

• Description:
  Authentication mechanisms ensure only authorised users access the application. When these mechanisms falter, attackers can impersonate users, steal sessions, or bypass login mechanisms altogether.

• Example:
  A web application allows users to log out but doesn't invalidate their session token. An attacker could then reuse this token to gain unauthorised access.

app.post('/logout', (req, res) => {
  // Not invalidating the session or token
  res.send("Logged out");
});

• Solution:
  Strengthen authentication processes. Utilise frameworks that handle session management securely and enforce practises like multi-factor authentication.

app.post('/logout', (req, res) => {
  req.session.destroy();  // Invalidate session
  res.send("Logged out");
});

Certainly, I'll continue with the detailed format for the remaining points:

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4. Broken Access Control

• Description:
  Access control mechanisms determine which users can perform certain actions or access particular resources. When these controls aren't robustly implemented, it could lead to unauthorised users gaining undue privileges, potentially compromising sensitive information or critical functionalities.

• Example:
  In an application, users with a regular role can inadvertently access an endpoint meant for admins, thus viewing sensitive admin data.

app.get('/admin/data', (req, res) => {
  // No checks for user roles
  res.send(adminData);
});

• Solution:
  Establish stringent role-based or attribute-based access control mechanisms. Middleware can be used to ensure that requests are checked for proper permissions before processing.

const jwt = require('express-jwt');

const checkAdmin = (req, res, next) => {
  const user = req.user;
  if (user.role !== 'admin') return res.sendStatus(403);
  next();
};

app.get('/admin/data', jwt({ secret: 'your_jwt_secret' }), checkAdmin, (req, res) => {
  res.send(adminData);
});

---

5. Server-Side Request Forgery (SSRF)

• Description:
  SSRF attacks allow attackers to make requests to other internal resources using the server's permissions. By exploiting endpoints that fetch data from other sources, an attacker might access internal networks, databases, or other services.

• Example:
  A web application has an endpoint for fetching and displaying the content of a URL. This can be manipulated to access internal resources.

const request = require('request');

app.get('/fetch', (req, res) => {
  const url = req.query.url;
  request(url, (error, response, body) => {
    res.send(body);
  });
});

• Solution:
  Sanitise and validate all incoming data, especially URLs. Ensure that requests can't be made to internal resources, and consider employing a deny list for certain IP ranges or domains.

const axios = require('axios');

const isSafeUrl = (url) => {
  // Implement URL validation logic
  // For instance, reject URLs pointing to 10.0.0.0/8, 172.16.0.0/12, etc.
};

app.get('/fetch', async (req, res) => {
  const url = req.query.url;
  if (!isSafeUrl(url)) return res.sendStatus(400);
  const response = await axios.get(url);
  res.send(response.data);
});

---

6. Security Misconfiguration

• Description:
  Security misconfigurations can arise from using default configurations, verbose error messages, unnecessary features, and more. Such oversights could inadvertently expose sensitive information, provide unintended access, or reveal system vulnerabilities to attackers.

• Example:
  A web application returns a verbose database error, revealing internal schema details or other sensitive information.

app.get('/data', (req, res) => {
  database.getData((err, data) => {
    if (err) return res.send(err);  // Exposing raw error
    res.send(data);
  });
});

• Solution:
  Regularly review and update configurations. Minimise the information in error messages shown to end-users and ensure all system components are appropriately secured.

app.use((err, req, res, next) => {
  // Generic error message to the client
  res.status(500).send('Something went wrong!');
  // Detailed error logging
  console.error(err.stack);
});

---

7. Insecure deserialisation

• Description:
  Deserialisation converts structured data into an object. Insecure deserialisation can enable attackers to execute malicious code or exploit application logic by feeding the application manipulated data.

• Example:
  An application takes serialised data from users and directly deserialises it, potentially leading to unwanted behaviours or vulnerabilities.

const maliciousData = req.body.data;
const obj = unserialize(maliciousData); // Using an insecure deserialization function

• Solution:
  Use safe serialisation and deserialisation libraries. Always validate and sanitise data before and after deserialisation.

const data = req.body.data;
const obj = JSON.parse(data);  // For JSON data

---

8. Sensitive Data Exposure

• Description:
  If stored or transmitted insecurely, sensitive data, such as passwords, credit card numbers, or personal information, is susceptible to interception by attackers.

• Example:
  An application stores users' passwords in plain text in its database, making it a goldmine for attackers if breached.

const plaintextPassword = req.body.password;
database.save({ password: plaintextPassword });

• Solution:
  Ensure that sensitive data is encrypted both in transit and at rest. Use up-to-date cryptographic methods and libraries to protect this data.

const bcrypt = require('bcrypt');
const saltRounds = 10;

bcrypt.hash(req.body.password, saltRounds, (err, hash) => {
  database.save({ password: hash });
});

---

9. Insecure Direct Object References (IDOR)

• Description:
  IDOR attacks involve manipulating input to access objects (like files or database entries) that an attacker shouldn’t be able to access.

• Example:
  A user changes their user ID in a URL or requests to access another user's profile or data.

app.get('/profile/:userId', (req, res) => {
  database.getUserById(req.params.userId, (err, user) => {
    res.send(user);
  });
});

• Solution:
  Always verify if the authenticated user has the proper permissions to access the targeted resource.

const checkUserOwnership = (req

, res, next) => {
  if (req.user.id !== req.params.userId) return res.sendStatus(403);
  next();
};

app.get('/profile/:userId', checkUserOwnership, (req, res) => {
  database.getUserById(req.params.userId, (err, user) => {
    res.send(user);
  });
});

10. Insufficient Logging and Monitoring

• Description: The absence of adequate logging and monitoring allows malicious activities to go unnoticed.

• Example: Not logging failed login attempts.

app.post('/login', (req, res) => {
  if (!isValidLogin(req)) {
    return res.status(401).send('Invalid credentials');
  }
  // ... rest of the login logic
});

• Solution:|
  Package: Winston or morgan for logging andexpress-rate-limit for rate-limiting repetitive requests.

const winston = require('winston');
const rateLimit = require('express-rate-limit');

const limiter = rateLimit({
  windowMs: 15 * 60 * 1000,  // 15 minutes
  max: 100  // limit each IP to 100 requests per windowMs
});

app.use(limiter);

app.post('/login', (req, res) => {
  if (!isValidLogin(req)) {
    winston.error('Failed login attempt for IP: ', req.ip);
    return res.status(401).send('Invalid credentials');
  }
  // ... rest of the login logic
});

Conclusion:
In the relentless battle between web security and malicious entities, awareness and proactiveness are our best defences. By understanding server-side vulnerabilities and their countermeasures, we can fortify our digital fortresses and ensure safer online experiences for all.