Alternative to GROUP_CONCAT

Context

The objective of this guide is to teach you how to bypass Web Application Firewall (WAF) restrictions on the GROUP_CONCAT function using alternative MySQL functions. To follow along, you are expected to have foundational knowledge of SQL functions, database aggregation, and techniques for bypassing MySQL WAFs.

Theory

GROUP_CONCAT Limitations in WAF Contexts

WAFs often impose restrictions on certain SQL functions, such as GROUP_CONCAT, to prevent data aggregation leaks that can lead to security vulnerabilities. Attackers may exploit these functions during SQL injection attacks to aggregate multiple rows of data into a single result string, posing a significant threat to data confidentiality.

To counteract these restrictions, attackers can identify which SQL functions are blocked and explore alternative aggregation methods that achieve similar outcomes without being flagged by the WAF.

Using JSON_ARRAYAGG as an Alternative

JSON_ARRAYAGG is a powerful MySQL function that aggregates values into a JSON array. This function can serve as an effective alternative to GROUP_CONCAT when you're attempting to perform SQL injection attacks under the radar of WAFs that block GROUP_CONCAT.

The core principle here is to replace GROUP_CONCAT with JSON_ARRAYAGG in your SQL payloads, maintaining your ability to aggregate data while circumventing WAF restrictions. This substitution allows the aggregation of data into a format (JSON) that is often less scrutinized by security mechanisms.

Practice

• Identify SQL injection point where GROUP_CONCAT is blocked by attempting to inject a payload using this function.

• Replace GROUP_CONCAT with JSON_ARRAYAGG in your SQL query to aggregate the data silently. Here is a command example:

  SELECT JSON_ARRAYAGG(column_name) FROM table_name WHERE condition;
  

• Verify if JSON_ARRAYAGG successfully bypasses the WAF by checking for a JSON array response including the intended data.

The expected outcome is to successfully bypass WAF restrictions using JSON_ARRAYAGG, accessing aggregated data without triggering security defenses.

Tools

• Burp Suite