To develop a Go-language Web application firewall (WAF), you need to start with core functions: 1. Request interception and parsing, and use the net/http or Gin and Echo framework to parse request parts before business logic; 2. Attack feature recognition, match SQL injection, XSS and other attacks through precompiled regular and OWASP rules; 3. Rule management and dynamic loading, support JSON/database storage and implement hot updates through API; 4. Logging and response processing, record interception details and return 403 responses, and support observation mode to avoid manslaughter.
If you plan to use Go to develop a Web Application Firewall (WAF), you need to start with the most core functions: intercepting malicious requests, identifying attack modes, and supporting flexible rule configuration. The Go language itself has obvious advantages in performance and concurrent processing, and is very suitable for this type of network middleware.
Here are some key links that you can't avoid:
Request interception and parsing
The first step of WAF is to "see" all HTTP requests. You can build middleware based on net/http package, or use more mature frameworks such as Gin and Echo to implement plug-in filtering mechanism.
- Put WAF before all business logic as a prefilter
- Resolve various parts of the request: URL, Headers, Query Params, Body, etc.
- Pay attention to Body buffered reading of POST/PUT requests (because it is read only once by default)
To give a simple example: if you want to check whether the User-Agent is empty, you need to extract the field from the header and determine whether it exists or matches the blacklist.
Attack feature recognition
The core capability of WAF lies in identifying common attack behaviors, such as SQL injection, XSS, command injection, etc. You need to build a set of rules engines to match these characteristics.
Common methods include:
- Regular expressions match sensitive keywords, such as
' or '1'='1,<script></script>, etc. - Use predefined rulesets, such as OWASP ModSecurity rules (can be used as a reference)
- Rating special character combinations and intercept them if they exceed the threshold.
Note: If the regular writing is not done well, it will slow down performance. It is recommended to compile the rules in advance and control the number and complexity of the rules.
Rule management and dynamic loading
The hard-coded rules are certainly not flexible enough. A good WAF requires hot updates to support rules, and is best configured remotely through the interface.
You might consider:
- Store rules in JSON files or databases
- Load at startup, check regularly for changes at runtime
- Provides REST interface for adding, deleting, and modifying rules
- Set enable status and priority for each rule
For example, you have added a new XSS attack detection rule, which can be sent to all WAF instances through the API and take effect immediately without restarting the service.
Logging and response processing
After discovering suspicious requests, in addition to intercepting, you also have to record them for subsequent analysis.
The log should at least include:
- Client IP and User-Agent
- Intercepted URL and request method
- Matched rule ID or name
- Timestamp and operation result (blocking/release)
As for the response, it is generally reasonable to return 403 Forbidden. You can also add a switch to make certain rules just record and not intercept them, and are used for observation stages.
Basically that's it. Using Go to make WAF is not complicated, but there are many details, especially when it comes to a trade-off between performance and accuracy. For example, you should avoid the impact of normal user access due to manslaughter, and you should also prevent the missed real attacks.
The above is the detailed content of Go Web Application Firewall (WAF) Development. For more information, please follow other related articles on the PHP Chinese website!
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