Skype for Business and proxy.pac file serious bug causes slow login

Occasional Contributor
Hello and glad to be a member of this community!

I have found a rather serious and annoying bug in SfB 1708 (and possibly any other version) and have also opened a case with Microsoft for this but I believe that I also need to report here.

So, if a Windows 7 x64 / Office ProPlus x86 system is configured to use a proxy auto configuration file (wpad.dat,proxy.pac) fetched via an http request the file is directly used by SfB and follows the rules inside the file BUT!

Takes 10 minutes to Sign In

And this is due to some specific rules in the proxy.pac file that if removed, resolve the issue.

If someone wants to try to reproduce it’s as easy as Creating a pac file with the below and publishing on a web server then setting Internet Explorer to use that file.

function FindProxyForURL(url, host) {
if (isResolvable(host))
return "DIRECT";
return "DIRECT";

As seen above, this directive will in essence never direct SfB to use a proxy. It’s just a plain Dirext connection.

Then try to Sign In with SfB and see the huge delay!

Unfortunately there is no way to direct SfB to another proxy file as it follows the system configuration so I wish there was an option to configure it with different settings than the rest of the OS.


2 Replies
I found some possibly relevant information here:

Although this is not describing the same issue, I will give it a try.
best response confirmed by Alexander Kanakaris (Occasional Contributor)

The solution that I implemented and works is below:


Essentially there is a parsing issue when Windows 7 are used. This shouldn't appear with Windows 10.