SQL Injection Testing: Vulnerabilities & How To Prevent SQL Injection Attacks

By Fortra's Digital Defense

The tester’s aim when performing a website or system test is to ensure that the product being tested is protected as much as possible. Application security testing is typically performed to secure these networks and systems. To perform this type of test, it is necessary to consider which attacks are most likely to occur. One of the most common types of attacks is SQL injection (SQLi). These are common attacks as a result of how serious and harmful the consequences are to your system. 


SQL Injection 

What is SQL Injection?

SQL injection is an application security weakness which allows attackers to control a database. This can allow attackers to get access and delete information, change a data-driven behavior, and many other undesirable exploitations. Tricking the application into sending unexpected SQL commands can make injections among the most common threats in information security. 

The primary goal for an injection is to inject a malicious SQL statement into system code. Even a single quote of malicious code injected into an SQL can invade a network or system. Each and every field of a website can be compared to a gate in its database. In the login form, the individual enters the login information including a username/password, in the search field they enter a search text, in the data saving form they enter information to be saved. All these indicated pieces of information go into an index.  

There are possibilities for some serious damage to happen to the database and the whole system instead of correct data if even a single quote of malicious code is entered. To perform an injection, users must use the SQL programming language. SQL (Structured Query Language) is used to get access to information held in an archive. This programming language code is being used as a malicious injection during a system or network attack. 

Since databases are used for practically all systems or networks in technology, SQL injection is one of the most popular attacks. Many applications use some form of index. An interface that accepts input for the use of performing tasks may include: 

  • Showing any relevant information such as credentials of the user with login information like a username and password, exposing any relevant functionality and data.
  • Saving info entered by an individual to a database. This could come in the form of usernames, a password, or other various pieces of info. For example, once the user fills up a form and submits it, the operation will proceed to save the necessary info. 


Threat Modeling

In a system exploit, injection attacks would allow attackers to tamper with existing data, spoof identity, cause repudiation issues like voiding transactions or changing balances, allow the complete disclosure of all info on the system, execute code to destroy data or make it unavailable, and become administrators of the server. 

SQL injection is common with ASP and PHP applications as a result of the prevalence of older functional interfaces. Applications like J2EE and ASP.NET are less likely to have easily exploited injection attacks due to the nature of programmatic interfaces available. 

The severity of an injection invasion is limited by the attacker’s skill. It would also be limited by the defense in depth countermeasures, including low privilege connections to a server. It is best treat an injection as a high impact severity.


Associated Risks in SQL Injection

Today, a database is typically used for almost every web system, as information needs to be stored in some form or location. As sensitive data is being stored in the database, there are more risks involved in the system’s security. If any personal website or blog info would be stolen, then there won’t be much damage when compared to the data that would be stolen from the banking system. 

An SQL injection attack can lead to extremely harmful consequences, as the main purpose of this intrusion is to exploit a system. For example, the following might result from an injection:

  • Hacking another person’s account information including username and password
  • Stealing and copying sensitive information from networks, systems, and websites
  • Changing the system’s sensitive information
  • Deleting sensitive information from systems
  • Having an individual login as another user, even under an alternative username or administrator
  • An individual could view private information like transaction details that an attacker could select from users
  • An individual can change a web application configuration and the information of other users
  • Having an individual modify the structure of a database table, and even delete a table
  • A user can select and take control of the server and execute commands at will

The risks listed above can be considered serious, as restoring a database can cost a fortune. It can cost your company their reputation and money to restore the lost system. Therefore, it is highly recommended to protect your system against this type of intrusion and select a reputable security test as a good investment in your product and company’s reputation. 


Risks of SQL Injection

SQL injection attacks have become a common issue in websites and applications. The flaw can be easily detected and exploited, so any site or software package with even a minimal user base is likely to be subject to an attempted injection attack. This attack is essentially accomplished by placing a select character into a data input to then place commands in the control plane. This data did not previously exist there before. This creates a flaw that depends on SQL injection and makes no real distinction between the control and data planes. 

Keep in mind that a test against possible attacks is good practice even if security testing was not planned. This way, your organization can protect and test the product against unexpected cases and malicious users. 


How Does the SQL Scanner Work?

As previously mentioned, the essence of an injection is to hack the database with malicious intent. To perform this form of injection test, your organization initially needs to find a vulnerable system and then send malicious code through the database. Malicious code will be sent and harmful actions may be performed in the database if this attack is possible for a system. 

Every single field of a web application is comparable to a gate in the database. Inputs that are usually entered in a field of the web application or system will go to the database query. Instead of entering correct data, attackers can execute any malicious code in the query, resulting in harmful consequences.  


SQL Injection Anatomy

Developers identify a SQL query to perform some action necessary for their program to function properly. The query has an argument so that only desired records are returned, and the value for that argument is provided by a user. These attacks function in two stages:

  1. The attacker tries to submit various unexpected values for the argument, observes a response, and determines a way to execute an attack. 
  2. The attacker provides a carefully crafted input value that will be interpreted as part of a SQL command when used as a query argument. The database will then execute the command as modified by the attacker. 


How Attackers Exploit SQLi Vulnerabilities

There are multiple techniques that can be used to exploit injection vulnerabilities in a web app. The types of SQL injection attacks that are commonly seen include:

  • Error-based Injection
  • UNION-based Injection
  • Blind Injection
  • Out-of-band Injection

Error-based SQL Injection

Although this attack is one of the most common types of injection vulnerabilities, it can be quite easy to determine. This type of injection attack relies on feeding unexpected commands or invalid input - typically through an interface - to cause the server to reply with an error that may contain details about a target. These include the operating system, structure, version, and even a return of complete query results. 

UNION-based SQL Injection

The UNION operator extends the results returned by the original query, which enables an individual to run two or more statements if they have the same structure as the original query. 

Blind SQL Injection

This type of injection attack does not show any error message, which is why it is known as a “blind” SQL injection. It is more difficult to exploit as it returns information when a web application is given payloads that return a “true” or “false” response from the SQL server. The attacker can try to extract sensitive information by observing the response. This type of injection attack has two different kinds of injection: boolean-based and time-based.

Boolean-based Blind SQL Injection

In this type of blind attack, a Boolean query causes the application to give a different response for a valid or invalid result in the system. This example works by enumerating the select characters from the text that needs to be extracted like a table name and column name one by one. 

Time-based Blind SQL Injection

This type of injection requires a specific time period to wait before a vulnerable application responds to an attacker. The time taken by the application to deliver the response is what determined the success of the attack. 

Out-of-band SQL Injection 

With this type of injection attack, the application shows the same response regardless of the input and the error. To retrieve the output response, a different transport channel such as HTTP requests or DNS resolution is used. It is important to note that an attacker needs to control saif HTTP or DNS server. 

SQL Injection Testing 

There are different ways to avoid injection vulnerabilities to limit the damage that is often caused by them. These methods include:

SQLi Discovery 

A SQL injection vulnerability can be detected by routinely testing applications by both using static and dynamic testing. 

Avoid and Repair 

An injection vulnerability can get repaired by using specific queries. These types of queries specify placeholders for parameters so that the database will always treat them as a data rather than part of a command. Prepare a statement and an object relational mapper to make this process easy for developers. 

Remediate SQLi Vulnerabilities 

These vulnerabilities can be remediated in legacy systems by escaping inputs before adding them to the query. Use this technique only where a similar facility and prepared statement are not available. 

How to Prevent SQL Injection Attacks

It is best practice to mitigate the impact of injection vulnerabilities by enforcing least privilege on an archive. Ensure that each application has its own index credentials, so that they have the minimum rights an application needs. 

Developers can enforce input validation and resort to a prepared statement in combination with other protection methods to mitigate an injection.

Each of the different methods can be implemented on the server side within a traditional approach to prevent injection attacks. Doing so will handle them as an input validation problem. Accept only select characters from an allowed list of safe values, or identify and escape a deny list of potentially malicious values.

Although this list can be a solid method for enforcing strict input validation rules, statements will require less maintenance and offer more security. Deny listing can be full of loopholes that make it ineffective at preventing injection attacks. For example, attackers can try to complete injection attacks including:

  • Target field that are not required
  • Finding ways to bypass the need for certain escaped meta-characters
  • Use stored procedures to hide the injected meta-characters

Manually escaping characters in input to SQL queries will not make your application completely secure from attacks, but it can certainly help. Another example commonly used in combating any injection attacks is to use stored procedures. Stored procedures fail to protect against many others even if they combat injection attacks. 

Stored procedures can often help prevent injection attacks by limiting the type of statement that can be passed to their parameters. However, there are many ways around the limitations and interesting statements that can still be passed to stored procedures. Stored procedures will not make your application completely secure against SQL injection attacks even if they prevent a possible exploit.


Other SQL Injection Strategies

Validating User-supplied Input

Validating user-supplied inputs is possible in two ways: blacklisting and whitelisting characters that are accepted or denied in the user input fields. Creating a list of select characters is an efficient method for SQL injection attacks. Once the whitelist is ready, the application should disallow all requests containing characters outside of it. 


Blacklisting is highly prone to failure, which is why it is not a recommended way to protect against SQLi attacks. It works only when a developer can ensure that the user input fields accept no special characters other than what is required. The result should be escaping all characters that may prove to be harmful. 

Prepare a Statement

Using a prepared statement may be used as a way to force queries at the front-end to be handled as the content of a parameter, not as part of the SQL query itself. An attacker cannot try to modify the backend query by inserting inputs at the front-end. 

Least Privilege Principle

This principle can prevent the user from running queries that require elevated privileges. Using this principle can result in a lower impact of the SQL injection attack. For example, an account that only has read access to the database may not be used to alter stored information if the account is compromised. 

Additional Security Layers

Solutions such as Web Application Firewalls (WAFs) can help provide an extra layer of security in protecting against SQL injections. WAFs inspect traffic and are able to determine whether the traffic is bad or not. Maintenance is required as signatures need to be updated. Otherwise, attackers can try to find a way to bypass a WAF. 


SQL Injection Attacks

SQL injection is one of the most common and dangerous forms of vulnerabilities. One simple mistake in the user validation process could cost an organization their entire archive. Several open source tools exist to make the job of the attacker easier by allowing them shell access or help dumping the archive. Following secure coding guidelines for writing SQL queries and adopting the best open source tools and practices can help developers avoid this security risk in their organization.

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About the Author

Our Vulnerability Research Team consists of credentialed (Security+, Network+, CISSP) cybersecurity experts with decades of combined experience in research, analysis, and the discovery of unknown vulnerabilities. 

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