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Defending Your WordPress Site from SQL injections


In the world of WordPress, website security is of paramount importance. One significant aspect that cannot be overlooked is the prevention and mitigation of SQL injection vulnerabilities in WordPress plugins. SQL injection, a prevalent and dangerous attack vector, can allow malicious actors to manipulate and exploit your website’s database, potentially leading to unauthorized access, data breaches, or even complete site compromise.

In this blog post, we will delve into the realm of SQL injection vulnerabilities in WordPress plugins, focusing on their impact and the steps you can take to mitigate them effectively. We will explore three types of SQL injection attacks: in-band, blind, and out-of-band, providing a comprehensive understanding of each technique and their potential consequences.

Furthermore, we will examine real-world examples of SQL injection vulnerabilities found in two popular WordPress plugins, “Paid Membership Pro” and “Perfect Survey.” By analyzing these cases, we can gain insights into the vulnerabilities and understand the inherent risks associated with unsanitized SQL queries in plugin code.
Our exploration will not only shed light on the vulnerabilities but also demonstrate how an attacker could exploit them to extract sensitive information, such as usernames, passwords, or other confidential data. However, it is crucial to note that these demonstrations are for educational purposes only, aiming to raise awareness about the potential risks and encourage better security practices.

Alongside the exploration of vulnerabilities, we will discuss the importance of proper mitigation techniques. We will highlight the significance of utilizing prepared statements, input validation, and proper sanitization methods like wpdb->prepare to prevent SQL injection attacks effectively. Mitigation techniques play a critical role in fortifying your WordPress site’s security and safeguarding it against potential threats.

By the end of this blog post, you will have a comprehensive understanding of SQL injection vulnerabilities, their potential impact, and the measures you can take to mitigate these risks effectively. Let’s dive in and empower ourselves with the knowledge to protect our WordPress sites from SQL injection attacks.

Types of SQL injection

In-Band SQL Injection

In an in-band SQL injection attack, the attacker typically exploits a vulnerability in the application’s input validation or sanitization mechanisms. They manipulate user-supplied input, such as form fields, URL parameters, or cookies, to inject malicious SQL code into the application’s database query.

In an in-band SQL injection attack, the attacker takes advantage of a vulnerability in the application’s input validation or sanitization mechanisms. By manipulating user-supplied input, such as form fields or URL parameters, they inject malicious SQL code into the application’s database query. This type of attack is commonly known as Classic SQL Injection or In-Band SQL Injection.

The attack unfolds in several steps. First, the attacker identifies an input field within the web application that lacks proper validation or sanitization. This could be any area where user input is accepted, such as a login form or a search box. Once a vulnerable input is discovered, the attacker proceeds to craft a malicious payload by inserting SQL code into the vulnerable input.

The injected SQL code is designed to manipulate the structure or behavior of the database query. By altering the intended behavior, the attacker gains the ability to perform various actions within the database. These actions may include bypassing authentication mechanisms, extracting sensitive data, modifying or deleting records, or even executing arbitrary commands on the database server.

The immediate feedback received from the application plays a crucial role in an in-band SQL injection attack. The application’s response to the injected SQL code provides valuable information to the attacker. This feedback can manifest as error messages, different responses, or even unexpected changes in the application’s behavior. By carefully analyzing the application’s responses, the attacker can gather insights into the database’s structure, including table names, column names, and other sensitive information.

Armed with the knowledge gained from the immediate feedback, the attacker can proceed to extract sensitive data from the database. By leveraging the information obtained through the in-band SQL injection attack, they can retrieve unauthorized data, potentially leading to data breaches, unauthorized access, or complete compromise of the application and underlying systems.

Blind SQL injection

Blind SQL Injection is a type of SQL injection attack where an attacker can inject malicious SQL code into a vulnerable application, but unlike in-band SQL injection, they do not receive immediate feedback or visible results of their injected code in the application’s response.

Blind SQL Injection attacks typically occur when an application processes user input in a way that does not directly expose the results of the injected code. This can happen if the application suppresses error messages or does not display query results on the web page. As a result, the attacker must find alternative methods to infer information about the database and extract data.

There are two main types of Blind SQL Injection:

  • Time-Based Blind SQL Injection: In a time-based blind SQL injection attack, the attacker injects malicious SQL code that introduces time delays into the SQL query. By analyzing the application’s response time, the attacker can determine whether the injected condition is true or false. For example, the attacker may inject a query that includes a WAITFOR DELAY statement and observe if the application’s response is delayed accordingly.
  • Boolean-Based Blind SQL Injection: In a boolean-based blind SQL injection attack, the attacker injects SQL code that relies on Boolean conditions to infer information. The injected code might exploit the application’s behavior by injecting conditions that, if true, result in a different application response compared to when the conditions are false. By analyzing the variations in the application’s responses, the attacker can deduce information about the database.

Blind SQL Injection attacks can be more challenging to exploit compared to in-band attacks because the attacker does not have immediate feedback on the success or failure of the injected code. Attackers must rely on techniques that involve trial and error, iterating through different payloads and analyzing the application’s responses to infer information about the database structure and contents.

Blind SQL Injection vulnerabilities can still have severe consequences, as attackers can gradually gather sensitive information, such as database schema details, table names, column names, or even extract data through a series of carefully crafted queries.

Out-Of-Band SQL injection

Out-of-Band SQL Injection is a type of SQL injection attack where an attacker is able to extract data from a database through a separate communication channel outside the normal response of the vulnerable application. Unlike in-band SQL injection, which relies on immediate feedback in the application’s response, out-of-band attacks leverage external interactions to retrieve data.

Out-of-band SQL Injection attacks often occur when the application is unable to directly communicate with the attacker’s machine or the attacker cannot directly observe the results in the application’s response. Instead, the attacker manipulates the application in a way that indirectly triggers data extraction or exfiltration through an alternate communication channel.

There are several methods commonly used in out-of-band SQL Injection attacks:

  • DNS Exfiltration: In DNS-based out-of-band attacks, the attacker injects malicious SQL code that exploits the application’s interaction with the Domain Name System (DNS). By manipulating the injected code, the attacker causes the application to perform DNS lookups to domains they control. The attacker can monitor DNS server logs to extract the requested data.
  • HTTP Request: In some cases, out-of-band attacks involve injecting SQL code that triggers HTTP requests to external servers controlled by the attacker. By monitoring the server logs or analyzing the incoming requests, the attacker can extract the desired data.
  • Email Notifications: Out-of-band attacks can also exploit the application’s capability to send email notifications. The attacker injects SQL code that causes the application to send emails to an address controlled by the attacker. The content of the emails can contain the extracted data or information that indirectly reveals sensitive details.

Out-of-band SQL Injection attacks can be challenging to execute and may require additional setup by the attacker. They typically require vulnerabilities that enable the application to interact with external systems or rely on the availability of specific features within the target application.

Vulnerabilities in “Paid Membership Pro” and “Perfect Survey plugins”

The “Paid Membership Pro” plugin and the “Perfect Survey” plugin, both widely used in WordPress, have been found to contain vulnerabilities that expose websites to blind SQL injection attacks. These vulnerabilities stem from the improper handling of user-supplied input when constructing SQL queries.

One of the primary issues with these plugins is the absence of proper sanitization and validation of user input before incorporating it into the SQL queries. Instead of utilizing the recommended method of using wpdb->prepare to prepare the SQL query, the plugins directly integrate the user input into the query string. This oversight opens the door for potential exploitation by attackers.

By crafting carefully constructed payloads and injecting them through user inputs, an attacker can exploit the unsanitized SQL queries in the “Paid Membership Pro” and “Perfect Survey” plugins. This can lead to unauthorized access to sensitive information, data breaches, and potentially even the compromise of the entire website.

It is crucial for plugin developers and website administrators to understand the importance of proper input validation and sanitization when constructing SQL queries. The use of wpdb->prepare or other similar methods helps prevent SQL injection vulnerabilities by separating the SQL code from user input and ensuring that inputs are treated as data, not executable code.

In the upcoming sections, we will demonstrate how these blind SQL injection attacks can be performed using SQLMAP in the “Paid Membership Pro” and “Perfect Survey” plugins, shedding light on the potential risks faced by websites that utilize these vulnerable plugins.

Paid Membership Pro < 2.9.8

In the “Paid Membership Pro < v2.9.8” plugin, there exists a vulnerable REST API route, specifically /pmpro/v1/order, which is designed to enable users to query membership information using a member code. When this API endpoint is called with a member code, it triggers the execution of the getMemberOrderByCode function, responsible for performing a database query to retrieve the corresponding membership details.

The critical issue lies in the implementation of the database query within the getMemberOrderByCode function. Unfortunately, the plugin developers have not taken appropriate measures to sanitize and validate the parameters used in the query. As a result, user-supplied input is integrated directly into the SQL query without proper sanitization, making the code susceptible to SQL injection attacks.

You can see the vulnerable code below.

The following image demonstrates the retrieval of the admin user’s username and password hash using SQLMAP in the context of “Paid Membership Pro”. The payload utilized for this operation is outlined below:

sqlmap --url "<URL>/?rest_route=/pmpro/v1/order&code=a" -p code --technique=T --dbms=mysql --batch --dump -T wp_users -C user_login,user_pass

In this SQLMAP payload, the --url parameter specifies the target URL with the appended query string parameter code=a. The -p code option indicates that the code parameter is the injection point. The --technique=T flag selects the technique to be used during the attack, with T representing time-based blind injection. The --dbms=mysql option specifies the database management system as MySQL. The --batch flag enables batch mode, while --dump instructs SQLMAP to extract data from the specified table. The -T wp_users and -C user_login,user_pass options specify the table and columns to be dumped, respectively.

The dumped user name and the password hash is shown below.

We can now utilize a password cracking tool such as hashcat to attempt password cracking by leveraging a wordlist containing commonly used passwords.

Image below shows the cracked password.

The SQL injection issue mentioned has been resolved by the “Paid Membership Pro” team in plugin versions 2.9.8 and above. Therefore, if you are currently using an older version, it is strongly recommended to update the plugin to ensure the security of your website.

Below is an updated version of the code where the vulnerability has been addressed by implementing proper input sanitization using wpdb->prepare.

Now, let’s shift our focus to the “Perfect Survey” plugin. In the following code snippet, it is evident that the SQL query lacks proper sanitization, similar to the previous case, resulting in a significant SQL injection vulnerability.

To exploit this vulnerability, we can leverage the admin-ajax API, which the “Perfect Survey” plugin uses to query survey questions based on the question ID. The SQLMAP payload for this attack is as follows:

sqlmap --url "<URL>/wp-admin/admin-ajax.php?action=get_question&question_id=1" -p question_id --answers="follow=y" --batch -v 0 --dbms mysql --dump -T wp_users -C user_login,user_pass

By executing this payload using SQLMAP, we can attempt to extract sensitive information from the database. The command instructs SQLMAP to target the specified URL with the given parameters, utilizing the question_id parameter for injection. The --answers="follow=y" flag instructs SQLMAP to automatically handle and follow prompts during the attack. The --batch flag enables batch mode, while -v 0 sets the verbosity level to zero to minimize output. The --dbms mysql flag specifies the database management system to be MySQL. The --dump option instructs SQLMAP to dump the contents of the specified table, wp_users, and the -C user_login,user_pass option specifies the columns to be extracted.

Unlike the “Paid Membership Pro” plugin, the “Perfect Survey” team has not yet addressed the identified vulnerability at the time of writing. Regrettably, the plugin has been flagged as outdated by the WordPress organizers.

In situations where official patches or updates are unavailable, manual application of a patch to the affected file becomes necessary. The applied patch is outlined below. Nevertheless, it is crucial to recognize that additional vulnerabilities may exist, highlighting the significance of conducting a comprehensive code review to ensure the plugin’s safety.

When manually patching files, exercising caution is of utmost importance. Incorrect modifications can introduce new issues or disrupt the functionality of the plugin. It is highly recommended to create a backup of the original file and rigorously test the patched version before deploying it in a production environment. This proactive approach mitigates the risk of unintended consequences.

After applying the patch, we can conduct a retest of the SQL injection vulnerability to confirm that data exfiltration is no longer possible through this exploit.

When it comes to safeguarding your site against potential SQL injection vulnerabilities, a fundamental step you can take is to modify the default table prefix from “wp_” to a less common value. To delve deeper into this topic, we recommend reading our blog post titled How to Set Up WP Hide. It is essential to note that changing the table prefix alone will make it more challenging to identify critical tables, but it does not provide complete mitigation of the issue.

To enhance overall security, conducting a comprehensive code review and thorough testing is crucial. In this regard, our team of experts at “Red Threat Cyber Security” specializes in assisting you with fortifying the security of your mission-critical site. By leveraging our expertise, you can ensure a robust defense against potential threats.


Securing your WordPress site against SQL injection vulnerabilities is of utmost importance in today’s digital landscape. Throughout this blog post, we have explored the various facets of SQL injection attacks in WordPress plugins, gaining insights into the different types of attacks and their potential consequences. By examining real-world examples from “Paid Membership Pro” and “Perfect Survey,” we have witnessed the dangers posed by unsanitized SQL queries and the need for robust security measures.

Our exploration has highlighted the significance of proper mitigation techniques in preventing SQL injection vulnerabilities. Utilizing prepared statements, input validation, and sanitization methods like wpdb->prepare are crucial steps in ensuring secure coding practices. By implementing these techniques, developers can significantly reduce the risk of SQL injection attacks and protect user data from unauthorized access.

However, it is important to remember that mitigation techniques alone are not enough. Regular updates, secure plugin development practices, and thorough code reviews are essential components of a comprehensive security strategy. By adopting these measures, WordPress site owners can minimize the likelihood of SQL injection vulnerabilities and bolster their overall security posture.

Remember, securing your WordPress site is an ongoing effort. Stay vigilant, keep your plugins up to date, and prioritize the implementation of secure coding practices. By doing so, you can safeguard your site, protect user data, and maintain the trust of your visitors. Together, we can create a more secure and resilient WordPress environment for all.