Types of Malicious Attacks on Web Applications

Web applications are used for online shopping, banking, communication, education, healthcare and business operations. Because they often store valuable information, they are common targets for cybercriminals.

A malicious attack on a web application occurs when an attacker attempts to access information, take control of an account, damage a website, steal money or disrupt a service.

Some attacks target weaknesses in the application’s code. Others target users, passwords, server settings, third-party software or application programming interfaces.

Understanding the most common types of attacks can help website owners, developers and businesses improve their security.

A cybersecurity professional monitoring a web application for malicious activity.

1. Broken Access Control Attacks

Broken access control happens when a web application does not properly control what users are allowed to view or do.

For example, a regular user may be able to view another customer’s account information by changing an identification number in a web address. In another case, a user may access an administrator page without having administrator permissions.

Attackers may exploit these weaknesses to:

• View private customer information.
• Edit another user’s account.
• Access administrator features.
• Download restricted files.
• Delete or modify important records.

To reduce this risk, every important action should be checked on the server. Applications should never rely only on hidden buttons or restrictions in the user interface.

An illustration showing restricted user accounts and administrator access levels.

2. SQL Injection Attacks

SQL injection occurs when an attacker places harmful database commands into an application input field.

If the application does not safely handle the input, the attacker may influence the database query. This can allow unauthorized access to customer records, login information or business data.

SQL injection may be used to:

• Read confidential information.
• Change database records.
• Delete stored information.
• Bypass login systems.
• Damage the operation of a website.

Developers can reduce SQL injection risks by using prepared statements, parameterized queries, safe database libraries and strict input validation.

A secure database protected from unauthorized application queries.

3. Cross-Site Scripting Attacks

Cross-site scripting, commonly called XSS, happens when an attacker causes a web application to display harmful code in a visitor’s browser.

This can happen when an application accepts user input and displays it on a web page without properly validating, sanitizing or escaping it.

Depending on the situation, an XSS attack may allow an attacker to:

• Steal session information.
• Change what a user sees on a page.
• Redirect visitors to harmful websites.
• Perform actions using a victim’s browser.
• Display fake login forms.

Applications can reduce XSS risks by safely encoding output, validating input, using content security policies and protecting cookies.

Security agencies have identified improper input validation and output handling as major causes of cross-site scripting vulnerabilities. [Secure by Design Alert: Eliminating Cross-Site Scripting … – CISA](https://www.cisa.gov/resources-tools/resources/secure-design-alert-eliminating-cross-site-scripting-vulnerabilities)

A browser protected against malicious scripts injected into a web page.

4. Cross-Site Request Forgery Attacks

Cross-site request forgery, also known as CSRF, tricks a logged-in user’s browser into sending an unwanted request to a web application.

For example, an attacker may attempt to make a user change an email address, update an account setting or submit a form without the user intentionally performing that action.

CSRF attacks are more likely to succeed when:

• The victim is already logged in.
• The application trusts browser requests automatically.
• Important actions do not require additional verification.
• The application does not use anti-CSRF tokens.

Developers can reduce this risk by using anti-CSRF tokens, secure cookie settings, origin checks and additional confirmation for sensitive actions.

A user account protected from unauthorized form submissions.

5. Brute-Force and Credential-Stuffing Attacks

In a brute-force attack, an attacker repeatedly tries different passwords until one works. Credential stuffing is similar, but it uses usernames and passwords stolen from previous data breaches.

These attacks are dangerous because many people reuse the same password on multiple websites.

Attackers may use stolen credentials to:

• Take over customer accounts.
• Access private messages.
• Steal stored payment information.
• Use accounts to send spam.
• Access business systems.

Web applications should use multi-factor authentication, rate limiting, account lockout protections, bot detection and strong password policies.

Login and password-reset systems should receive the same level of protection as other sensitive parts of an application.

A secure login screen using a password and multi-factor authentication.

6. Session Hijacking

Session hijacking occurs when an attacker obtains a user’s session information and uses it to act as that user.

Web applications commonly use session cookies to remember authenticated users. If a session cookie is exposed, stolen or poorly protected, an attacker may be able to access the account without knowing the password.

Session hijacking can happen through:

• Unsecured connections.
• Cross-site scripting vulnerabilities.
• Malware on a user’s device.
• Insecure cookie settings.
• Long-lasting or predictable sessions.

Applications should use HTTPS, secure cookies, short session lifetimes, session rotation and logout invalidation.

A secure browser session protected with encryption and secure cookies.

7. Malicious File Upload Attacks

Many web applications allow users to upload profile pictures, documents, videos or other files. If upload features are not properly protected, attackers may upload harmful content.

A dangerous file may attempt to:

• Execute unauthorized code.
• Install malware.
• Replace website files.
• Expose private directories.
• Use the server to attack other systems.

Secure file-upload systems should verify file types, limit file sizes, rename uploaded files, store them outside executable directories and scan them for malware.

File extensions alone should not be treated as proof that a file is safe.

A secure file-upload system scanning documents before storing them.

8. Path Traversal Attacks

Path traversal occurs when an attacker manipulates a file path to access files outside the directory intended by the application.

If successful, this type of attack may expose configuration files, application code, passwords or private customer information.

Applications should avoid accepting unrestricted file paths from users. Developers should use safe file identifiers, restrict access to approved directories and validate all file-related input on the server.

A server filesystem protected against unauthorized directory access.

9. Server-Side Request Forgery Attacks

Server-side request forgery, commonly called SSRF, occurs when an attacker tricks a web server into sending requests to a location chosen by the attacker.

This can be especially dangerous when the server can access internal services that are not available directly from the internet.

An SSRF attack may allow attackers to:

• Access internal applications.
• Read cloud service information.
• Scan private network services.
• Reach administrative interfaces.
• Use the server to send requests to other systems.

Developers can reduce SSRF risks by restricting outbound requests, allowing only approved destinations, blocking internal network ranges and carefully validating URLs.

A web server blocking unauthorized requests to internal network services.

10. Security Misconfiguration

Security misconfiguration happens when a website, server, database or cloud service is not securely configured.

Common examples include:

• Default administrator passwords.
• Unnecessary services left enabled.
• Publicly accessible backups.
• Detailed error messages shown to visitors.
• Outdated software.
• Open cloud storage.
• Incorrect file permissions.
• Missing security headers.

Security configuration should be reviewed regularly. Unused services should be disabled, software should be updated and sensitive information should never appear in public error messages.

A web server dashboard showing secure configuration settings.

11. Denial-of-Service Attacks

A denial-of-service attack attempts to make a web application unavailable by sending excessive traffic or requests.

When many compromised devices participate in the attack, it is called a distributed denial-of-service attack, or DDoS attack.

DDoS attacks can cause:

• Slow page loading.
• Website downtime.
• Unavailable login services.
• Higher infrastructure costs.
• Loss of customer trust.

Protection may include traffic filtering, rate limiting, content delivery networks, caching, load balancing and DDoS protection services.

Applications should also protect expensive actions, such as searches, file processing and report generation, from unlimited automated requests.

A website protected from a large volume of malicious traffic.

12. API Attacks

Application programming interfaces, or APIs, allow websites and applications to exchange data. APIs are essential for mobile apps, online stores, payment systems and software integrations.

However, an insecure API may expose sensitive information or allow unauthorized actions.

Common API weaknesses include:

• Broken object-level authorization.
• Weak authentication.
• Excessive data exposure.
• Unrestricted resource consumption.
• Missing rate limits.
• Improper API inventory management.
• Unsafe use of third-party APIs.

API security requires authentication, authorization checks, input validation, rate limiting, logging and regular testing.

OWASP’s API Security Top 10 includes risks such as broken object-level authorization, broken authentication, unrestricted resource consumption and unsafe consumption of APIs. [OWASP Top 10 API Security Risks – 2023](https://api-security.owasp.org/editions/2023/en/0x11-t10/)

An API gateway checking authentication and authorization before allowing access.

13. Malware and Web Shell Attacks

Malware attacks occur when attackers place harmful software on a website or server. One example is a web shell, which may give an attacker remote access to server functions.

A compromised website may be used to:

• Redirect visitors to harmful websites.
• Display spam content.
• Steal customer information.
• Send phishing emails.
• Host malicious downloads.
• Attack other websites.

Website owners should keep applications, plugins and themes updated. They should also use strong administrator passwords, limit file permissions, scan files and maintain clean backups.

A malware scanner checking website files for suspicious code.

14. Supply-Chain Attacks

A supply-chain attack targets software, plugins, libraries or services that a web application depends on.

Instead of attacking the main website directly, attackers may compromise a third-party component. When the compromised component is installed or updated, the malicious code may reach many applications.

Businesses can reduce supply-chain risks by:

• Using trusted software sources.
• Keeping an inventory of dependencies.
• Removing unused plugins and libraries.
• Reviewing software updates.
• Using dependency scanning tools.
• Restricting third-party permissions.
• Monitoring unexpected changes.

A software supply chain being monitored for unsafe third-party components.

How to Protect a Web Application

No single security tool can protect every web application. Effective protection requires secure development practices, regular maintenance and continuous monitoring.

Important security measures include:

• Use HTTPS for all pages and services.
• Require multi-factor authentication for administrator accounts.
• Use strong password policies.
• Keep the application, plugins and server software updated.
• Validate and sanitize user input.
• Use prepared database queries.
• Apply least-privilege access controls.
• Protect cookies and sessions.
• Back up website files and databases.
• Monitor logs for unusual activity.
• Scan websites for malware.
• Test the application before releasing changes.
• Train staff to recognize phishing and suspicious activity.

A complete web application security strategy using multiple layers of protection.

Conclusion

Web applications can face many types of malicious attacks, including broken access control, SQL injection, cross-site scripting, credential attacks, file-upload attacks, SSRF, API abuse, malware and denial-of-service attacks.

Attackers often succeed because of simple weaknesses such as outdated software, weak passwords, incorrect permissions or insufficient input validation.

The best defense is a layered security approach. Developers should follow secure coding practices, website owners should maintain their software and businesses should monitor their applications for unusual activity.

Security should be treated as an ongoing process rather than a one-time task. Regular updates, testing, backups and monitoring can significantly reduce the risk of a successful web application attack.