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8 Critical Web Application Vulnerabilities and How to Prevent Them

May 30, 2022
Oliver Moradov

What Are Web Application Vulnerabilities?

A web application vulnerability is any system flaw that an attacker can exploit to compromise a web application. Web vulnerabilities differ from other common vulnerabilities like asset flaws or network vulnerabilities because web applications require the ability to communicate and interact with multiple users from different networks. The accessible nature of a web application makes it an easy target for a hacker. Continuous security testing is critical to identify security vulnerabilities and protect your organization.

In this article:

Common Types of Web Application Vulnerabilities

1. SQL Injection

Many applications use Structured Query Language (SQL) to manage communications with the database. SQL vulnerabilities allow attackers to insert malicious SQL commands to exfiltrate, modify, or delete data. Some hackers use SQL to gain root access to the target system. 

SQL injection attacks target servers that hold critical data used by web applications or services. They are particularly dangerous when they expose critical or sensitive data, such as user credentials and personal information. The most common vulnerability enabling SQL injection attacks is using unsanitized user inputs. It is important to strip out any element in user-supplied inputs that the server could execute as SQL code. 

Related content: Read our guide to SQL injection

2. Cross-Site Scripting (XSS) 

XSS attacks are similar to SQL injection attacks and involve the injection of malicious scripts into websites or web applications. The point of difference is that the malicious code runs in the browser only when the user visits a compromised website or app. Attackers often carry out XSS attacks by injecting code into input fields that the target page runs when visitors view the page (e.g., embedded JavaScript link). 

An XSS attack can expose user data without indicating a compromise, impacting business reputation in the long run. Attackers can steal any sensitive data sent to the infected app, and the users may remain oblivious. 

Related content: Read our guide to XSS

3. Cross-Site Request Forgery (CSRF)

A CSRF attack occurs when an attacker forces the victim to perform unintended actions on the web application. The victim first logs into the web app, which has deemed the user and browser trustworthy. Therefore, the app will execute malicious actions that the attacker tricks the victim into forwarding a request to the web app. The motivation for CSRF ranges from simple pranks to enabling illicit financial transactions. 

Related content: Read our guide to CSRF

4. Session Fixation

A session fixation attack involves forcing a user’s session ID to a specified value. Depending on the target web application’s functionality, attackers may use various techniques to fix session ID values. Examples of session fixation techniques include cross-site scripting exploits and reusing HTTP requests. 

First, an attacker fixes the victim’s user session ID. Then, the user logs in and inadvertently exposes the online identity. The attacker can then hijack the victim’s user identity using the fixed session ID value. 

Any web application that authenticates users with sessions is vulnerable to session fixation attacks without adequate defenses. Web apps that use session IDs typically use cookies, though they can also use hidden form fields or URLs. Cookie-based user sessions are the most popular and the easiest to compromise. Most fixation attacks target cookie-based sessions.

5. Local File Inclusion (LFI)

An LFI attack exploits the dynamic file inclusion mechanisms in a web application. It may occur when a web application takes user input, such as a parameter value or URL, and passes it to a file inclusion command. An attacker can use this mechanism to trick the app into including a remote file containing malicious code. 

Most web application frameworks enable file inclusion, which is useful primarily to package shared code into different files for later reference by the application’s main modules. If a web app references a file for inclusion, it might execute the code in the file explicitly or implicitly (i.e., by calling a specific procedure). The application could be vulnerable to LFI attacks if the module-to-load choice is based on HTTP request elements.

Related content: Read our guide to LFI

6. Security Misconfigurations

Security misconfigurations are some of the most serious web application vulnerabilities because they provide attacks with opportunities to infiltrate the application easily. Attackers could exploit a wide range of security configuration vulnerabilities. These include unchanged default configurations, data stored in the cloud, ad hoc or incomplete configurations, plaintext error messages containing sensitive information, and HTTP header misconfigurations. Security misconfigurations may be present in any operating system, library, framework, or application. 

Related content: Read our guide to security misconfiguration

7. XML External Entity (XXE) Processing

An XXE attack occurs when an attacker abuses widely used features in XML parsers to gain access to remote or local files, typically resulting in Denial of Service (DoS). Attackers can also use XXE processing to carry out SSRF attacks, which force the web application to make external, malicious requests. XXE can also enable attackers to scan ports and execute malicious code remotely. 

Related content: Read our guide to XXE

8. Directory Traversal

Directory traversal attacks, or backtracking, involve exploiting how the web application receives data from a web server. Web apps often use Access Control Lists (ACLs) to restrict user access to specific files within the root directory. A malicious actor can identify the URL format the target application uses for file requests. 

Related content: Read our guide to directory traversal

Solutions for Preventing Web Application Vulnerabilities

The most effective way to prevent web application vulnerabilities is to test your applications for vulnerabilities and remediate them. Here are four ways of identifying critical vulnerabilities in web applications.


Static Application Security Testing (SAST) solutions scan source code for vulnerabilities and security risks. Many web applications incorporate code scanning at multiple stages of development, including while committing new code to the codebase and building new releases.

SAST is usually rules-based and scan results can contain false positives, so the results must be carefully analyzed and filtered to identify real security issues.

Related content: Read our guide to SAST


Dynamic Application Security Testing (DAST) can test an application that is deployed in a staging or production environment, and execute its code to check for vulnerabilities. Automated DAST tools find vulnerabilities by sending numerous requests, including unexpected and malicious inputs, to applications, and analyzing the results to identify security vulnerabilities.

Manual penetration testers usually perform similar tests to those performed by DAST tools, using tools like Burp Suite, Fiddler, and Postman. 

Related content: Read our guide to DAST


Interactive application security testing (IAST) solutions combine dynamic testing (similar to DAST tools) with static analysis (similar to SAST tools) to help identify and manage security risks in web applications. 

IAST solutions monitor application execution and gather information about functionality and performance. They identify vulnerabilities in real time by deploying agents and sensors that inspect running applications, and continuously analyzing all application interactions. In addition, many IAST solutions incorporate software configuration analysis (SCA) to identify open source components and frameworks and discover known vulnerabilities.

Related content: Read our guide to IAST

Penetration Testing

Penetration testing is a security technique that combines human security expertise with dynamic scanning tools to find vulnerabilities in web application security mechanisms.

Penetration testers operate from an attacker’s perspective. They perform reconnaissance, attempt to exploit vulnerabilities, gain unauthorized access, and demonstrate their ability to steal data or disrupt services. However, they operate ethically, without causing actual harm to the organization and within the scope of an agreement with the web application owner.
Related content: Read our guide to penetration testing

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