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When you’re using Azure WAF and Azure Active Directory OpenID Connect, you can experience the WAF blocking on the rule: SQL Comment Sequence Detected.

This is the real solution, please don’t use the solution that Microsoft Azure give you, it’s very dangerous.

Microsoft Azure - Dangerous way

When you ask the support, they escalate and the only solution that they give you is: you need to disable this rule.

WTH!!!

They want us to disable the rule for the entire WAF so the entire traffic.

It’s easy to see that Microsoft will never change about stupid thing and also about their own services.

The Right Way: Custom Rule

We just need to allow the traffic on a specific setting: a value at the beginning of a cookie.

It’s not a joke, I use it on production and it works.

The logic:

If: String

Match:

  • variable RequestHeaders
  • Header name: Cookie

Operation: is

Operator: Begins with

Transformations: keep empty

Match value: .AspNetCore.OpenIdConnect.

Then: Allow traffic

Screenshot from Azure Portal

Never forget

When you need to write and enable custom rules, keep in mind to restrict to required URLs when it’s not affecting all endpoints.