Nginx HTTP firewall and WAF

Nginx is a high-performance HTTP server widely used in Web development. It is often used to build reverse proxy, load balancing, dynamic caching and other Web solutions. Due to its reliability, security and scalability, more and more web applications adopt Nginx as their basic service. However, due to the widespread nature and openness of web applications, they are often targets of hackers and malicious attacks. In such an environment, protecting the security of web applications is particularly important. Therefore, the Nginx development team proposed two important security features: HTTP firewall and WAF.

1.HTTP Firewall

HTTP Firewall (HTTP Firewall) is a security measure that can identify and block malicious attacks based on the HTTP protocol. Under the HTTP protocol, each request contains an HTTP header, so an attacker can attack by modifying the HTTP header. For example, an attacker might send an HTTP request with malicious parameters to exploit a vulnerability in an application, and an HTTP firewall could handle such a request.

Nginx’s HTTP Firewall is an open source module that helps web applications protect against some of the most common web attacks, such as cross-site scripting (XSS), SQL injection, file inclusion, request spoofing, and more. It can track visitors' HTTP requests and intercept, filter and defend against malicious requests.

Here are some configurable options and examples for HTTP firewall:

• client_header_buffer_size: Specifies the size of the client HTTP header buffer.
• client_body_buffer_size: Specifies the size of the client HTTP body data buffer.
• client_max_body_size: Specifies the maximum length allowed by the HTTP body data sent by the client.
• http2_max_field_size: Specifies the maximum length of the HTTP/2 request header field.
• http2_max_header_size: Specifies the maximum size of the HTTP/2 request header.

The above are only a small part of the configuration options, which need to be set specifically according to the needs of the web application. However, it should be noted that HTTP firewalls can only provide basic security protection measures and still need to be supplemented by other functions, such as WAF.

2.WAF

WAF (Web Application Firewall) is a firewall specially designed for Web applications. It can not only intercept and block attacks based on the HTTP protocol, but also target Web applications. Application-specific vulnerabilities are protected. WAF usually runs between the web server and the application, intercepting malicious requests, attack payloads and harmful traffic.

Nginx’s WAF module is an open source application that can be customized through custom rules. It detects and blocks malicious traffic and attack payloads reaching web applications, such as SQL injection, cross-site scripting, OS attacks, and HTTP protocol attacks. The WAF module also supports custom rules files to meet more specific application needs. In addition to relying on regular rule packets, it can also be combined with other third-party rule engines, such as ModSecurity.

Here are some examples of WAFs:

• blacklist_by_ip: Reference blacklist to block web requests from malicious IP addresses.
• block_sql_injection: Detect and block SQL injection attacks.
• block_xss: Detect and block cross-site scripting attacks.
• block_brute_force: Detect and block brute force attacks.
• block_file_inclusion: Detect and block file inclusion attacks.

A specific set of rules needs to be developed based on the specific needs and security threats of the web application.

Summary

Nginx’s HTTP firewall and WAF functions are a complete web protection system. When configured correctly, it can greatly improve the security of web applications and protect the organization's information security. However, it should be noted that the security issue cannot be completely solved, and continuous evaluation and testing are still required to ensure its effectiveness and adaptability.

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