SQL injection occurs when external data becomes part of an SQL command and changes its meaning. In a Joomla extension, it can allow unintended reading, modification or deletion of database content.
Where the risk comes from
Building SQL strings from unchecked input creates the risk. Input can originate in URL parameters, forms, headers or previously stored data. Browser-side validation is not a security boundary.
Safer Joomla queries
Use prepared queries and parameter binding through the Joomla database API for values. Data is passed separately from the query structure. Choose column names, sorting directions and other syntax elements from an allowlist, because a normal value parameter cannot replace them.
Validate types and permitted ranges as well. Removing quotation marks or applying an HTML filter does not make arbitrary SQL safe. Give the database account only the privileges the application needs.
Website maintenance
Keep Joomla and extensions updated, remove unused components and maintain usable backups. If a vulnerability is suspected, inspect the specific handler and relevant logs without publishing secrets or full queries containing personal data.
A firewall may block some suspicious requests, but cannot repair unsafe query construction in the application.
Conclusion
The main defence separates data from commands. Parameter binding, allowlisted syntax and limited privileges work together.