I had to install a local instance of MediaWiki this afternoon. After setting up a web server, downloading the latest version and completing the installation process all worked well except for the following two lines at the top of the browser:

Notice: A non well formed numeric value encountered in …includesCryptRand.php on line 382
Notice: A non well formed numeric value encountered in …includesCryptRand.php on line 383

 

Change line 285 from:

$bytes .= $iv;

to:

$buffer .= $iv;

Then I had to logout, clear my cache, then all was fine. I’ll update here if I find out more details about the exact causes of this error/bug.