An SQL injection (SQLi) attack occurs when an attacker manipulates a web application's client input data to inject malicious SQL (Structured Query Language) code into the application's database queries. SQL injection attacks rank third on OWASP's Top 10 vulnerabilities list, and tend to disproportionately impact both PHP and ASP.NET applications (though not exclusively). 

What makes SQL injection attacks so dangerous?

The goal of a SQL injection attack is to gain unauthorized access to a database, retrieve, modify, or delete data, and potentially perform administrative actions on that database. 

SQL injection attacks also allow attackers to spoof identities, cause non-traceable issues such as voiding transactions or changing balances, disclose all system data on the system, or even become administrators of the server. 

Finally, SQL injection attacks can have the following public-facing consequences: 

  • Privacy violations

  • Regulatory violations and compliance failure

  • Reputational damage

  • Legal action and payouts to impacted users

  • Extended remediation times

Based on these ramifications and the commonality of SQL injection attacks, these threats continue to be very real for web application developers and users reliant on their services. 

Read More: Most Common Website Security Threats

How does an SQL injection attack work?

We've discussed how SQL injection attacks use malicious SQL queries to impact databases. However, there are three primary ways to orchestrate an SQL injection attack: 

  • In-band SQL injections (most common) – Attackers leverage error-based injection attacks to deduce a database's structure from server error messages (and therefore probe for weaknesses), or use the UNION SQL operator to combine multiple select statements into one HTTP response. The communications channel used in the attack also transmits its results. 

  • Out-of-band SQL injections (least common) – Attackers use different communication channels to execute an attack and compile the results. Server performance or stability can impact whether this method is plausible. 

  • Blind (or inferential) SQL injections – An attacker attempts to learn about a database's structure by sending payloads to the server and analyzing its responses. These attacks take longer and work through either boolean or time-based injections. 

Can HAProxy help prevent SQL injection attacks?

Yes! HAProxy Enterprise, HAProxy ALOHA, and HAProxy Enterprise Kubernetes Ingress Controller ship with our HAProxy Enterprise WAF (web application firewall) to protect against application threats like SQLi, XSS, and more. Industry-leading WAF accuracy and performance lets us efficiently detect malicious threats without causing a bottleneck. Plus, HAProxy features a battle-hardened codebase with over 20+ years of development and optimization.