This might happen if your LImeSurvey installation cannot properly determine the IP address to a server misconfiguration.

In application/helpers/common_helper.php around line 4709
modify the existing code to look like that

if (!filter_var($sIPAddress, FILTER_VALIDATE_IP)) {
    var_dump($_SERVER); var_dump($sIPAddress); die();
    return 'Invalid';

and run the survey. This will dump some information on screen - if your screen is just white look at the HTML source.

Let us know what output you get.

Feedback please?

Thanks for the hint, it helped me find a local fix in the GetIPAddress function in common_helper.

On Azure (my host) $_SERVER['HTTP_X_FORWARDED_FOR'] returns a non-empty string, though not a valid ip address.

My local solution was to promote $_SERVER['REMOTE_ADDR'] higher up the ifelse block so this value is picked up.

A proper 'fix' would probably be to have the ifelse block checking for a valid ip address, not just checking if !empty?

Just out of curiosity: What string did it return?

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=26530

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=26531

I actually didn't note it at the time (just observed the non-empty invalid ip condition) but just ran a test and on Azure I get (real ips hidden):

HTTP_CLIENT_IP: (blank)

REMOTE_ADDR: 999.99.99.999

HTTP_X_FORWARDED_FOR: 999.99.99.999:99999

so the HTTP_X_FORWARDED_FOR includes a port number which could, presumably, be stripped off. The IP itself is identical to REMOTE_ADDR in my case.

Interestingly, I have read elsewhere (https://www.jamescrowley.co.uk/2007/06/19/gotcha-http-x-forwarded-for-returns-multiple-ip-addresses/) that in certain conditions, HTTP_X_FORWARDED_FOR can contain a sequence of comma-separated IP addresses.