NAXSI means Nginx Anti XSS & SQL Injection. NAXSI is an open-source, high performance, low rules maintenance WAF for NGINX. Technically, it is a third party nginx module, available as a package for many UNIX-like platforms. This module, by default, reads a small subset of simple (and readable) rules containing 99% of known patterns involved in website vulnerabilities. For example, <, | or drop are not supposed to be part of a URI.