Using mod_rewrite to redirect based on query string parameter-CodePudding

I am trying to get something working with mod_rewrite, but am not entirely sure it's even possible.

Say I have some request like:

https://www.example.com?h=somerandomvalue&u=www.another.example/content

I'd like to take the value of the u parameter and rewrite the request using this value, so from the above example request, I'd like to rewrite it to be

https://www.another.example/content

So basically, request:

https://www.example.com?h=somerandomvalue&u=www.another.example/content

Redirects to:

www.another.example/content

Is this possible? I've seen other examples where people are capturing and using parameters as part of a rewritten path but I have not seen anything in the way of redirecting to an entirely new domain using the provided parameter.

Any help or guidance here is very much appreciated!

CodePudding user response：

I've seen other examples where people are capturing and using parameters as part of a rewritten path

Yes, this is possible. The basic principle is the same:

RewriteEngine On

RewriteCond %{QUERY_STRING} (?:^|&)u=([\w./-]{6,})(?:&|$)
RewriteRule ^$ https://%1 [QSD,R=302,L]

%1 is a backreference to the capturing group in the preceding CondPattern. ie. the value of the u URL parameter.

([\w./-]{6,}) is just a very rudimentary check to match a semi-valid URL. This can be improved.

The (?:^|&) prefix on the regex ensures we only match the u URL parameter and not any URL parameter that simply ends in u.

This only redirects requests for the root, as in your example. A malicious user could turn your site into a relay to forward traffic.

However, without further validation of the URL being redirected to this is open to abuse and should not be used.