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I'm an under a DDoS attack though I have cloud flare..

I found out that the attacker is accessing the server using query strings "?a=randomnumber"

I don't use query strings in my website so I need to block any IP that tries to add query string in the request

It would be preferable if this can be set in mod_security or CloudFlare

Thanks in advance

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You might want to see if you can do such filtering within cloudflare. Filtering it on your own servers with mod_security won't do much good to stem the DDoS. – Falcon Momot Mar 21 '14 at 9:10

Is the attacker hitting your IP directly at all?

It is really hard to give additional guidance without knowing your pricing plan (the WAF might also help, if you are on a paid plan).

Some other tips for dealing with a DDoS

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