Yet another bug in this month’s Windows patches: Proxy bug knocks out some internet connections

There’s a reason why I wait before recommending that you install patches, yes?

News came yesterday afternoon that every.single.Windows.patch released since the “optional, non-security, C/D Week” patch at the end of February introduces a newly acknowledge bug:

Devices using a proxy might show limited or no internet connection status

Devices using a manual or auto-configured proxy, especially with a virtual private network (VPN), might show limited or no internet connection status in the Network Connectivity Status Indicator (NCSI) in the notification area.  This might happen when connected or disconnected to a VPN or after changing state between the two. Devices with this issue, might also have issues reaching the internet using applications that use WinHTTP or WinInet. Examples of apps that might be affected on devices in this state are as follows but not limited to Microsoft Teams, Microsoft Office, Office365, Outlook, Internet Explorer 11, and some version of Microsoft Edge.

According to Microsoft, this bug was introduced in the “optional, non-security, C/D Week” patch for February. If you’re running Win10 1903 or 1909, that’s KB 4535996.

English translation: If you’ve installed any of the Windows updates since last February’s switch to MS-DEFCON 3, you’ve been bitten.

There have been three bad patches: The usual Patch Tuesday cumulative update, KB 4540673 for Win10 1903 and 1909; the emergency, notoriously buggy cumulative update KB 4551762 that was supposed to fix the SMBv3 bug; and KB 4541335, which is the next-to- penultimate “optional, non-security C/D Week” patch for Win10 1903 and 1909. [Correction: We’ll have optional, non-security, C/D Week patches in both April and May. Oh boy.]

If you’re using some other version of Windows, the KB numbers will be different.

Microsoft says “We are working on a resolution and are targeting a Microsoft Catalog only release of an out-of-band update to resolve this issue by early April.” English translation: If you were trusting enough to install any Windows patches since Feb’s switch to MS-DEFCON 3, and you hit a problem connecting to the internet, try rolling back the patch.Or “You might be able to mitigate the issue by restarting your device.”

The problem is odd enough that I haven’t seen it in action. But if your internet connection keeps dropping, you should definitely look at rolling back the buggy update(s). There’s nothing in those patches that needs to be installed, like, right now.

And fer heaven’s sake, don’t voluntarily put your machine in the “cannon fodder” category. Sit back, relax, wait for the problems to appear. And watch the MS-DEFCON level.