What is a Website Vulnerability and How Can it be Exploited?

Websites experience multiple attacks per day. A website vulnerability is a weakness or misconfiguration in a website or web application code that allows an attacker to gain some level of control of the site, and possibly the hosting server. Most vulnerabilities are exploited through automated means, such as vulnerability scanners and botnets. Cybercriminals create specialized tools that scour the internet for certain platforms, like WordPress or Joomla, looking for common and publicized vulnerabilities. Once found, these vulnerabilities are then exploited to steal data, distribute malicious content, or inject defacement and spam content into the vulnerable site.

Types Of Website Vulnerabilities

There are five common types of website vulnerabilities that are frequently exploited by attackers. While this isn’t an exhaustive list of all the possible vulnerabilities a determined attacker may find in an application, it does include some of the most common vulnerabilities websites contain today.

SQL Injection Vulnerabilities (SQLi) – SQL injection vulnerabilities refer to areas in website code where direct user input is passed to a database. Bad actors utilize these forms to inject malicious code, sometimes called payloads, into a website’s database. This allows the cybercriminal to access the website in a variety of ways, including:

• Injecting malicious/spam posts into a site
• Stealing customer information
• Bypassing authentication to gain full control of the website

Due to its versatility, SQL injection is one of the most commonly exploited website vulnerabilities. It is frequently used to gain access to open source content management system (CMS) applications, such as Joomla!, WordPress and Drupal. SQL injection attacks, for example, have even been linked to a breach of the U.S. Election Assistance Commission and a popular video game forum for Grand Theft Auto, resulting in exposed user credentials.

Cross-Site Scripting (XSS) – Cross-site scripting occurs when attackers inject scripts through unsanitized user input or other fields on a website to execute code on the site. Cross-site scripting is used to target website visitors, rather than the website or server itself. This often means attackers are injecting JavaScript on the website, so that the script is executed in the visitor’s browser. Browsers are unable to discern whether or not the script is intended to be part of the website, resulting in malicious actions, including:

• Session hijacking
• Spam content being distributed to unsuspecting visitors
• Stealing session data

Some of the largest scale attacks against WordPress have been from cross site-scripting vulnerabilities. However, XSS is not limited only to open source applications. Recently, a cross-site scripting vulnerability was found in gaming giant Steam’s system that potentially exposed login credentials to attackers.

Command Injection – Command injection vulnerabilities allow attackers to remotely pass and execute code on the website’s hosting server. This is done when user input that is passed to the server, such as header information, is not properly validated, allowing attackers to include shell commands with the user information. Command injection attacks are particularly critical because they can allow bad actors to initiate the following:

• Hijack an entire site
• Hijack an entire hosting server
• Utilize the hijacked server in botnet attacks

One of the most dangerous and widespread command injection vulnerabilities was the Shellshock vulnerability that impacted most Linux distributions.

File Inclusion (LFI/RFI) – Remote file inclusion (RFI) attacks use the include functions in server-side web application languages like PHP to execute code from a remotely stored file. Attackers host malicious files and then take advantage of improperly sanitized user input to inject or modify an include function into the victim site’s PHP code. This inclusion can then be used to initiate the following:

• Deliver malicious payloads that can be used to include attack and phishing pages in a visitors’ browsers
• Include malicious shell files on publicly available websites
• Take control of a website admin panel or host server

Local File Inclusion (LFI), like remote file inclusion, can occur when user input is able to modify the full or absolute path to included files. Attackers can then use this vector to gain, read or write access to sensitive local files— for example, configuration files containing database credentials. The attacker could also perform a directory traversal attack, amending an included file path to review the back end and host server files, exposing sensitive data. A local file inclusion attack has to potential to become a remote file inclusion attack if, for example, the attacker is able to include log files that were previously seeded with malicious code by the attacker through public interaction.

These types of vulnerabilities are frequently used to launch other attacks, such as DDoS and cross-site scripting attacks. They have also been used to expose and steal sensitive financial information, such as when Starbucks fell victim to an inclusion attack leading to a compromise of customer credit card data.

Cross-Site Request Forgery (CSRF) – Cross-site request forgery attacks are less common, but can be quite jeopardous. CSRF attacks trick site users or administrators to unknowingly perform malicious actions for the attacker. As a result, attackers may be able to take the following actions using valid user input:

• Change order values and product prices
• Transfer funds from one account to another
• Change user passwords to hijack accounts

These types of attacks are particularly vexing for ecommerce and banking sites where attackers can gain access to sensitive financial information. A CSRF attack was recently used to seize all control of a Brazilian bank’s DNS settings for over five hours.

Mitigating and Preventing Vulnerabilities

There are easy steps you can take to mitigate and prevent vulnerabilities from allowing hackers to gain unauthorized access to your website.

Update your applications – The first critical step in securing your website is to ensure all applications and their associated plugins are up to date. Vendors frequently release imperative security patches for their applications and it is important to perform these updates in a timely manner. Malicious actors stay in the loop on open source application news, and are known to use update notices as a blueprint for finding vulnerable websites. Subscribing to automatic application updates and email notifications on critical patches will help you stay one step ahead of the attackers. For more information, check out our article, How to Secure Your Open Source Application.

Use a Web Application Firewall (WAF) – Web application firewalls are the first line of defense against those probing your website for vulnerabilities. Web application firewalls filter out bad traffic from ever accessing your website. This includes blocking bots, known spam or attack IP addresses, automated scanners, and attack based user input. For more information, check out our article Web Application Firewalls and Content Delivery Network – A Double Whammy For Hackers.

Use a malware scanner – Your last line of defense is the use of a reputable automated malware scanner. It is recommended you find one that can automatically identify and vulnerabilities and remove known malware. To learn more about how automated scanners work, check out our video, How SiteLock SMART Works.

More advanced programmers may opt to manually review their code and implement PHP filters to sanitize user input. This includes methodologies such as limiting image upload forms to only .jpg or .gif files, and whitelisting form submissions to only allow expected input.

Understanding the types of vulnerabilities that hackers may attempt to use to exploit your web applications is an important first step to securing your website. Vulnerabilities can have dire consequences for not only your website and server, but for your customers’ data as well.

Check back with the SiteLock blog each week for more website security tips and information.