SQL injection (SQLi) remains a leading threat to web applications globally. According to research from Positive Technologies, SQLi was the most common vulnerability found in web apps in 2021, impacting 37% of organizations. This post will provide an in-depth guide on how to thoroughly test for dangerous SQL injection flaws.
What is SQL Injection and Why Does it Matter?
SQL injection involves inserting malicious SQL syntax and commands into application entry points like web forms and API endpoints. By manipulating the original SQL query, attackers can gain unauthorized access to and even modify sensitive information in the backend database.
Successful SQL injection can have devastating impacts, including:
- Unauthorized exposure of highly sensitive data like healthcare records, financial details, intellectual property, etc.
- Alteration or destruction of critical data through malicious INSERT, UPDATE or DELETE queries.
- Compromise of backend database servers to steal database contents or launch further attacks.
- Compromise of middle tier application servers through code injection or execution of stored procedures.
- Denial of service by overloading database resources or crashing database processes.
Major SQL injection breaches, such as the 2015 IRS breach exposing over 700,000 tax records, demonstrate how damaging these attacks can be. The 2022 OWASP Top 10 lists injection as the #1 threat to web applications for good reason.
Common SQL Injection Attack Techniques
Here are the most common methods attackers use when probing for SQLi vulnerabilities:
By terminating a query with a semicolon and starting a new one, the attacker can "stack" multiple queries into a single input. For example:
SELECT * FROM users; DROP TABLE users
This technique can allow very dangerous actions like deleting tables, modifying data, disabling firewalls and more with just one input.
Error-Based SQL Injection
Here the attacker enters unusual inputs aimed at triggering SQL errors that reveal sensitive details about the database structure and contents. This informs later malicious queries. For example:
‘ OR 1=1 --
May generate an error revealing the database version, application user, and other details.
Boolean-Based Blind SQL Injection
Boolean conditions are entered to extract data one bit at a time. Based on the different responses for TRUE or FALSE queries, the application‘s behavior reveals the value of each bit. An example:
‘ OR SUBSTRING(Version(), 1, 1) > ‘5
Out-of-Band SQL Injection
Out-of-band SQLi uses built-in database functionality like DNS or HTTP requests to "exfiltrate" query results to an external destination. This allows extraction of data even when the app behavior doesn‘t reveal content directly.
Time Delay SQL Injection
Adding database commands like WAITFOR DELAY or sleep() can be used for blind SQLi. By measuring delays in responses, the attacker can infer true or false conditions to extract data.
Comprehensive SQL Injection Testing Methodology
While automated scanners help, manual testing remains essential for thoroughly assessing SQLi risk. Organizations should adopt a methodology like the following:
Text Input Testing
- Attempt common malicious strings like single quotes, comment operators, semicolons, SQL keywords, etc.
- Check for concatenation issues by adding mathematical operators like 1+1=2
- Test for multiple parameter pollution like foo.php?id=1;id=2
- Verify multi-step processes by injecting stored payloads in earlier steps
Numeric Input Testing
- Use mathematical operators like 1 OR 1=1 and 1‘ OR ‘1‘=‘1
- Concatenate non-numeric strings like ‘foo‘+ ‘bar‘
- Leverage CAST()/CONVERT() to string together text
Boolean Input Testing
- Flip values with NOT or ! to evaluate for blind SQLi
- Force TRUE with OR 1=1 and FALSE with AND 1=2
Dropdowns, Radio Options
- Tamper with underlying values rather than visible text
- Intercept and manipulate selected parameters during submission
Test Across Injection Contexts
- Evaluate SELECT, INSERT, UPDATE, DELETE and other statements
- Check column names, table names, JOIN clauses, subqueries
- Test within stored procedures by manipulating procedure arguments
Test Authentication Bypasses
- Attempt bypassing login with ‘ OR 1=1– payloads
- Check for ID manipulation on admin screens
- Test for horizontal/vertical privilege escalation
Perform Input Fuzzing
Fuzzing involves manipulating inputs with random data to trigger unexpected behaviors and errors.
- Leverage tools like SQLmap and Sqlninja to auto-fuzz fields
- Feed extremely long strings, mix cases, encode/escape characters
- Develop custom fuzzing scripts to maximize coverage
Test Blind SQL Injection Scenarios
- Evaluate time delays by injecting WAITFOR DELAY
- Check for DNS/HTTP outbound requests signifying blind exfiltration
- Review logs for pingbacks, errors pointing to blind SQLi
Automated SQL Injection Scanning
While manual testing provides the most comprehensive analysis, automated scanners help identify the largest breadth of potential issues quickly. SQLMap is one of the most popular free scanners. Commercial tools like Acunetix, AppScan, and Netsparker also provide automated SQLi discovery.
When leveraging scanners, ensure thorough validation of findings to avoid false positives. Note scanners may miss complex or second order SQLi flaws. Use credentials for deeper insight into authenticated content.
Remediating SQL Injection Vulnerabilities
Here are leading methods for preventing exploitable SQLi flaws:
- Validate and sanitize all user-supplied input before passing to SQL queries
- Use parametrized queries or prepared statements that separate data from code
- Implement role-based access controls limiting database permissions
- Escape user input with security encoding libraries
- Limit database access to only the necessary IP addresses and accounts
- Patch and update database servers and applications regularly
Web application firewalls (WAFs) can also provide real-time defenses against SQLi attacks.
This comprehensive guide outlines an effective methodology for SQL injection discovery, along with leading remediation strategies. However, organizations should integrate both automated and manual testing into their secure development lifecycles. Proactively finding and fixing SQLi vulnerabilities before deployment is the best way to protect critical web applications and data assets.