SQL injection has been a major security risk since the early days of the internet. Find out what's at risk, and how cybersecurity pros can defend their organizations.
Few things terrify IT security professionals--and the organizations they protect--as much as data theft. In a single moment, a company's private data, customer records, employee IDs, and myriad other types of confidential data can be lifted from internal servers. A moment more, and that data is available for sale to the highest bidder.
One of the most common methods of stealing sensitive data is SQL injection (SQLi), which targets security vulnerabilities in web applications in order to inject a malicious SQL statement into the database that stores the web app's records.
It's essential that not only IT security professionals, but also the decision makers they protect, understand the risk of this security threat. This article is also available as a download, SQL injection attacks: A cheat sheet for business pros (free PDF).
What are SQL injection attacks?
Structured Query Language, or SQL, is a method of managing relational databases that was first conceived of in the 1970s. Since then, it has become the standard in database management systems (DBMS) and can be found in countless organizations around the world.
When the rise of internet web applications that connected to SQL databases became commonplace, it took no time at all for SQL injection attacks to become reality. Since first being discovered in 1998, SQLi has been the bane of almost every organization with a data-driven web app.
SQLi works, at least on the surface, in a very straightforward manner: An attacker submits a malicious SQL statement in a fillable field that exploits a vulnerability in the web app's SQL implementation.
If successful, the malicious SQL statement could dump the entire contents of a database, or select data like customer records, employee ID/password combinations, or anything else the targeted database contains. SQLi can also give an attacker administrator access to a database, allowing them to delete or modify data.
Depending on the nature of the SQL database, an SQLi attack can even give an attacker access to the operating system of the machine that hosts it, which can allow the attacker to gain access to other network resources.
SQL injections typically come in one of three forms: Classic SQLi (aka in-band SQLi), blind SQLi (aka Inference SQLi), and out-of-band (OOB) SQLi (aka DMS-specific SQLi).
Classic SQLi attacks are the most common and simplest form of SQLi. Classic attacks can occur whenever an SQL database allows users to submit an SQL statement. They come in two varieties:
- Error-based SQLi, which involves getting a web app to throw an SQL error that gives the attacker either information about the structure of the database or the particular information they're seeking.
- UNION-based attacks, which use the SQL UNION operator to determine specifics of the database's structure in order to extract information.
Blind SQLi attacks can be one of several different types of attacks, like error-based or UNION-based attacks, with the major difference being that the attacker isn't presented with an error message or any other kind of text to indicate the success or failure of their attack.
Blind attacks do, however, cause a web app to behave in different ways, depending on how the database responds to the SQL query. Attackers can then infer the structure of the database based on how the web app responds, allowing them to build a copy of the database character by character.
Because blind attacks reconstruct a database one character at a time, they are considered incredibly time consuming. The larger the database, the slower the response, which can make blind attacks impractical in many situations.
Out-of-band SQLi is a much less common approach to attacking an SQL server. It relies on certain features of an SQL database to be enabled; if those features aren't, the OOB attack won't succeed.
OOB attacks involve submitting a DNS or HTTP query to the SQL server that contains an SQL statement. If successful, the OOB attack can escalate user privileges, transmit database contents, and generally do the same things other forms of SQLi attacks do.
A fourth type of SQLi attack exists, but it was excluded from the list above because it involves combining SQLi attacks with other cyberattacks.
Called compound SQLi, these attacks involve using SQLi alongside cross-site scripting, denial of service, DNS hijacking, or insufficient authentication attacks. Pairing SQLi with other methods of attack gives hackers additional ways to avoid detection and circumvent security systems.
The end result of all these different forms of SQLi is the same: The theft of sensitive data that can not only endanger an organization, its employees, and its customers, but also erode trust in that organization's ability to keep confidential data safe.
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Who is at risk for an SQL injection attack, and what can happen to victims?
Organizational risk for an SQLi attack only requires meeting two simple criteria: Have a website, and having that website interact with an SQL database.
Without proper security in place, and in light of reports that some industries face over 1,000 cyberattacks a day, it's easy to imagine falling victim to an SQLi attack.
While any website relying on an SQL database can be subject to SQLi attacks, data-driven web apps are particularly tempting targets to hackers because of all the information they collect and store.
A data-driven web application is any app that changes its behavior based on the data a user inputs. Examples of data-driven applications include:
- Survey apps;
- report-generating apps;
- search apps;
- guest books;
- workflow applications;
- apps that generate notifications/reminders; and
- social media websites.
All of those types of web applications--and more--are potentially at a higher risk of SQLi attack.
With all of that data potentially up for grabs, it's easy to see what can become of organizations that suffer an SQLi attack. In particular, effects from successful SQL injection can include:
- An attacker creating a copy of the entire database (or specific portions);
- an attacker spoofing login credentials, impersonating a user, or even bypassing authentication entirely;
- modification of the database (e.g., changing, deleting, or adding records);
- theft of non-database files located in the DMBS' file system;
- execution of operating system commands that give an attacker access to other assets on the network that hosts the SQL database; and
- knocking the target web application/DBMS offline.
Those direct results of a successful SQLi attack are big enough problems on their own, but they aren't the only thing to consider--there's also the long-term fallout. Sale of confidential data on the dark web, loss of customers, recovery costs, erosion of trust--all of those outcomes and more can be the result of a successful SQLi attack.
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What are examples of successful SQL injection attacks?
SQL injection attacks have been plaguing the internet for over 20 years; in that time, many high-profile attacks and vulnerability discoveries have occurred.
- In 2002, a vulnerability was discovered on fashion brand Guess' website that exposed the names, credit card numbers, and expiration dates of over 200,000 customers.
- In 2006, hackers alleged to be from Russia broke into the Rhode Island state government website and stole over 4,000 credit card numbers.
- In 2007, a hacker going by rEmOtEr used an SQL injection attack to deface Microsoft's UK website. The attack didn't result in the theft of any data.
- In 2008, Oklahoma's Sexual and Violent Offender Registry was found to be vulnerable to an SQLi attack that allowed attackers to download over 10,000 offender records (including social security numbers).
- In 2009, the US government charged Albert Gonzalez and two co-conspirators with using SQLi attacks to steal over 130 million credit card numbers from 7-Eleven and several other companies.
- In 2011, hackers affiliated with Anonymous used SQLi to take down the website of IT security firm HBGary after its CEO claimed he had uncovered the identities of Anonymous members.
- In 2012, hackers from Team GhostShell published 36,000 sets of personal records belonging to students, faculty, and staff at over 53 universities that they stole using SQLi.
- In 2013, the RedHack collective used SQLi to break into a Turkish government website and erase people's debts to various government agencies.
- In 2014, security researchers were able to use a blind SQLi attack to steal user data and gain administrative access to automaker Tesla's website.
- In 2015, crowdfunding site Patreon was hacked using an SQLi attack. The breach was so serious that attackers didn't just get password data and donation records--they were able to steal Patreon's source code.
- In 2016, a 10-year-old Finnish boy named Jani found an SQLi vulnerability that allowed him to delete comments on other Instagram users' accounts.
- In 2017, the Illinois State Board of Elections voter registration database was hacked using an SQLi attack.
- In 2018, a vulnerability found in Cisco's Prime License Manager (now patched) allowed attackers to edit the license management database and gain elevated shell privileges on vulnerable systems.
- In 2019, flaws discovered in the website of popular video game Fortnite could allow attackers to gain access to user accounts via an SQLi attack.
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How can I prevent an SQL injection attack against my organization?
Make no mistake--SQL injection is incredibly dangerous and surprisingly commonplace. Fortunately, protecting your website or web app against SQLi isn't difficult to do.
For starters, use an SQLi probing tool like Tyrant-SQL to find any vulnerabilities your site or app may have. It can be difficult to narrow down what you're at risk for and running an app like Tyrant can make finding weaknesses much easier. Doing this initial step isn't strictly necessary, but it can give you a better picture of what you're up against.
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As for protection steps, OWASP's SQLi prevention page has an excellent rundown of how to defend yourself (as well as more details and examples). Note: These strategies can be used to protect other databases, like XPath and XQuery, as well. Here's an overview of what OWASP recommends.
1. Use prepared statements instead of dynamic queries
Prepared statements with parameterized queries should be how all database queries are written. Parameterization means that all SQL code involved in the query has to be defined beforehand, which means the database will be able to distinguish between code and user input.
If an attacker tries to input a malicious SQL statement, the database will treat the statement as data, not code, and the query won't be turned into a malicious one.
2. Use stored procedures
Using stored procedures is similar to using prepared statements--at least from the standpoint that both involve defining valid SQL statements beforehand. The difference between stored procedures and prepared statements is where the SQL code lives: In the case of prepared statements, SQL code is stored in the web app itself, whereas stored procedures live in the database and are called by the web app.
There are instances where stored procedures can be unsafe, particularly if dynamic SQL generation is used inside stored procedures. Avoid this if possible; if dynamic SQL generation is necessary, be sure that stored procedures are using input validation or proper escaping to prevent the injection of malicious code.
Stored procedures aren't as foolproof as prepared statements. Whenever possible, opt for prepared statements over stored procedures.
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3. Use input validation
In cases where some SQL code is a necessary part of user input, it's essential to create a whitelist of valid SQL statements. Only create a list of the most essential statements to avoid unvalidated statements ending up in a query.
Input validation alone isn't enough to protect an SQL database, but it should be used in all cases as an additional layer of protection.
4. Escape all user-supplied input
Escaping SQL input has the effect of eliminating the threat posed by certain characters in SQL statements. Depending on the kind of escape function used, SQL input statements will be edited to prepend a "\" or other character in front of certain characters in order to prevent malicious commands from executing correctly.
This is considered a last-ditch method of preventing SQLi attacks. By itself, escaping isn't reliable and is prone to error, especially if an escape function isn't coded correctly. Only use escaping if other prevention methods aren't possible.
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Additional defense methods
OWASP also recommends limiting database account privileges, especially for application accounts. While granting admin access to these accounts can make an application run smoothly, it also opens the door for SQLi by giving users admin access to the database.
In addition, it can be helpful to use different user accounts for different web applications in order to limit what a particular account has access to. Further, limiting read access to specific fields can prevent a successful SQLi attack from extracting information, leaving an attacker with only a small piece of database contents that render it useless.
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