What is SQL Injection Attack?
SQL Injection attacks (or SQLi) alter SQL queries, injecting malicious code by exploiting application vulnerabilities.
Successful SQLi attacks allow attackers to modify database information, access sensitive data, execute admin tasks on the database, and recover files from the system. In some cases attackers can issue commands to the underlying database operating system.
This article focuses on the anatomy of SQL injection attacks. To learn more, including how to prevent attacks, see our complete guide to SQL injection.
In this article, you will learn:
- Real-Life SQL Injection Attack Examples
- How Does a SQL Injection Attack Work?
- Impact of SQL Injection Attacks
- SQL Injection Code Examples
Real-Life SQL Injection Attack Examples
Over the past 20 years, many SQL injection attacks have targeted large websites, business and social media platforms. Some of these attacks led to serious data breaches. A few notable examples are listed below.
Breaches Enabled by SQL Injection
- GhostShell attack—hackers from APT group Team GhostShell targeted 53 universities using SQL injection, stole and published 36,000 personal records belonging to students, faculty, and staff.
- Turkish government—another APT group, RedHack collective, used SQL injection to breach the Turkish government website and erase debt to government agencies.
- 7-Eleven breach—a team of attackers used SQL injection to penetrate corporate systems at several companies, primarily the 7-Eleven retail chain, stealing 130 million credit card numbers.
- HBGary breach—hackers related to the Anonymous activist group used SQL Injection to take down the IT security company’s website. The attack was a response to HBGary CEO publicizing that he had names of Anonymous organization members.
Notable SQL Injection Vulnerabilities
- Tesla vulnerability—in 2014, security researchers publicized that they were able to breach the website of Tesla using SQL injection, gain administrative privileges and steal user data.
- Cisco vulnerability—in 2018, a SQL injection vulnerability was found in Cisco Prime License Manager. The vulnerability allowed attackers to gain shell access to systems on which the license manager was deployed. Cisco has patched the vulnerability.
- Fortnite vulnerability—Fortnite is an online game with over 350 million users. In 2019, a SQL injection vulnerability was discovered which could let attackers access user accounts. The vulnerability was patched.
How Does a SQL Injection Attack Work?
There are several types of SQL injection—here are a few common variants.
SQL injection based on user input
A basic SQL injection attack uses user inputs. Web applications accept inputs through forms, which pass a user’s input to the database for processing. If the web application accepts these inputs without sanitizing them, an attacker can inject SQL statements via form fields and delete, copy, or modify the contents of the database.
SQL injection based on cookies
Another approach to SQL injection is modifying cookies to “poison” database queries. Web applications often load cookies and use their data as part of database operations. A malicious user, or malware deployed on a user’s device, could modify cookies, to inject SQL in an unexpected way into the backend database.
SQL injection based on HTTP headers
Server variables such HTTP headers can also be used for SQL injection. If a web application accepts inputs from HTTP headers, fake headers containing arbitrary SQL can inject code into the database.
Second-order SQL injection
These are possibly the most complex SQL injection attacks, because they may lie dormant for a long period of time. A second-order SQL injection attack delivers poisoned data, which might be considered benign in one context, but is malicious in another context. Even if developers sanitize all application inputs, they could still be vulnerable to this type of attack.
Impact of SQL Injection Attacks
Here are a few examples of the harm SQL injection attacks can cause to an organization, if successful:
- Steal credentials—SQL injections can be used to find user credentials. Attackers can then impersonate these users and use their privileges.
- Access databases—attackers can use SQL injections to gain access to the information stored in a database server.
- Alter data—attackers can use SQL injections to alter or add new data to the accessed database.
- Delete data—attackers can use SQL injections to delete database records, including drop tables.
- Access networks—attackers can use SQL injections to access database servers with operating system privileges. The attacker can then attempt to access the network.
SQL Injection Code Examples
Let’s look at two common examples of SQL injection attacks. They are based on code provided by the OWASP project.
Example 1: Injecting Malicious Statement into Form Field
This is a simple SQL injection attack based on user input. The attacker uses a form that requires first name and last name as inputs. The attacker inputs:
- First name:
- Last name:
The SQL statement that processes the form inputs looks like this:
select id, firstname, lastname from authors
Once the attacker injects a malicious expression into the first name, the statement looks like this:
select id, firstname, lastname from authors where firstname = 'malicious'ex' and lastname ='newman'
The database identifies incorrect syntax due to the single apostrophe, and tries to execute the malicious statement.
Here is code from OWASP showing how to prevent this attack, by sanitizing the input.
String firstname = req.getParameter("firstname");
String lastname = req.getParameter("lastname");
String query = "SELECT id, firstname, lastname FROM authors WHERE firstname = ? and lastname = ?";
// Using a PreparedStatement to take the user’s query and sanitize it
// by setting it as a string, instead of directly passing it to DB
PreparedStatement pstmt = connection.prepareStatement( query );
pstmt.setString( 1, firstname );
pstmt.setString( 2, lastname );
ResultSet results = pstmt.execute( );
Example 2: Exploiting Concatenation Weakness
In this example, the following code obtains the current username, and searches for items matching a certain item name, where the owner is the current user.
string userName = ctx.getAuthenticatedUserName();
string query = "SELECT * FROM items WHERE owner = "'"
+ userName + "' AND itemname = '"
+ ItemName.Text + "'";
After combining the username and item name, the code creates the following query:
SELECT * FROM items
WHERE owner =
AND itemname = ;
The problem here is that the original code uses concatenation to combine data. The attacker can use a string like
‘name’ OR ‘a’=’a’ as the item name.
‘a’=’a’ is a condition that always evaluates to true, so the SQL statement will be true for all items in the table.
The SQL statement becomes:
SELECT * FROM items
WHERE owner = 'john'
AND itemname = 'name' OR 'a'='a';
Which is the same as:
SELECT * FROM items;
This means the query will return the data of the entire table, giving the attacker unauthorized access to sensitive data.
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