Nginx allowed characters inside full URL / URI and ARGS

lists at lists at
Fri Jul 14 23:54:59 UTC 2017

I took the opposite approach. You put a funny character in the URL, you get a 444.  I only allow underscore and hypen.

For a while, I was getting fuzzed. Maybe a year ago it was a thing. ‎Nothing bad happened, which I would say is a tribute to Nginx. I just returned 404s, but I figured I better trap this behavior before my luck runs out.

  Original Message  
From: c0nw0nk
Sent: Friday, July 14, 2017 12:58 PM
To: nginx at
Reply To: nginx at
Subject: Nginx allowed characters inside full URL / URI and ARGS

So I have been using Lua to iron out a few dilemmas and problems lately.

Does anyone know what characters Nginx accepts inside URL's

I am achieving a higher cache HIT ratio by modifying the URL's with Lua but
it also helps in preventing unwanted forms of DoS.

Here is my code :

local function fix_url(str)
return str:gsub("[+/=]", {["+"] = "+", ["/"] = "/", ["="] = "="})
--Needs some regex to remove multiple occurances of characters

ngx.var.modified_url = fix_url(ngx.var.request_uri) --Remove UN-wanted
duplicated characters that users are trying to bypass cache with. 

ngx.var.modified_url = string.lower(ngx.var.modified_url) --make all
lowercase to further increase cache HIT ratio

Now what I need to do is to introduce some regex to my gsub string in order
to remove multiple occurrences of those characters.

Example :

Good Link :

Bad Link :

You will notice that the good link is very friendly where as the Bad Link
will have the same contents served as the good link but is incredibly
dynamic and bypasses the cache each time. (What is how people are launching
their DoS attacks)

Any help on this little project would be fantastic :)

Posted at Nginx Forum:,275500,275500#msg-275500

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