Azure Web Application Firewall (WAF) REGEX for Match Variable Selector

[Sibba_Sailor]

Hi Experts,

We are trying to migrate our WAF solution to Azure WAF, and some validation rules use REGEX to match the Variable Selector. We are trying to implement the same on Azure WAF and are not sure if that is supported. The Azure Application Gateway WAF document does not cover that.

Basically what we are trying to achieve is, to implement this (attached image):

1. Match type: String
2. Match variable: PostArgs
3. Post args selector: arg\d{1,4}
4. Followed by Operation and Action

I am not sure if this is supported as the Azure Application Gateway WAF document does not mention it. We need a way to implement this rule so that it can cover multiple arg## instead of us having to create one rule for each. It is going to be difficult when we have, let's say, 100 args (arg1, arg2, arg3,......, arg100) or more.

Is it supported on Azure Application Gateway WAF? If not, what are the other ways/workaround to implement the same?

Thanks in advance!

[#2]

@Sibba_Sailor 

I didn't try but I believed yes as per REGEX supported

[#3]

The answer is Yes, Azure WAF does support Regular Expressions (regex) for defining validation rules, so you should be able to implement your current rule in Azure WAF as well. Below are the steps to create a validation rule using regex in Azure WAF:

Open the Azure Portal and navigate to your Application Gateway instance.
In the left-hand menu, click on "Web application firewall".
Click on "Managed rules".
Click on "Add rule".
In the "Validation rule" section, select "Custom rule".
In the "Match conditions" section, select "Post args".
In the "Post args selector" field, enter your regex pattern: "arg\d{1,4}".
In the "Operator" and "Action" fields, enter the desired values for your rule.
Save the rule.

Hope that helps!

[#4]

Hi Shanker,

The field allows us to put the RegEx for Post Args Selector but I am not sure if it is supported as I could not test it. The Azure documentation does not mention the support of RegEx for the Selector (https://learn.microsoft.com/en-us/azure/web-application-firewall/ag/custom-waf-rules-overview#select...).

Were you able to implement and test it successfully?

Also, take a look at the Question that I had posted for the same that says it is not currently supported.
https://learn.microsoft.com/en-us/answers/questions/1192824/azure-web-application-firewall-(waf)-reg...