Windows does Microsoft updates thru Its own web explorer.

https://www.bing.com/search?q=Microsoft+8+updates&qs=n&form=QBRE&sp=-1&pq=microsoft+8+updates&sc=8-19&sk=&cvid=92B390994F6B4A45981712942D9C075E

pryprsn said

I don't see the latest Windows patch for Meltdown & Spectre (KB4056894) available for download.

Here's the related Microsoft article, in case it helps: https://support.microsoft.com/en-us/help/4056894/windows-7-update-kb4056894 According to the article, (quote) Due to an issue with some versions of Anti-Virus software, this fix is only being made applicable to the machines where the Anti virus ISV have updated the ALLOW REGKEY. <snip> This update will be downloaded and installed automatically from Windows Update. If you are having problems with this update or with Windows Update in general, You should contact a Windows forum such as windowsbbs.com or answers.microsoft.com for assistance. You should mention your Antivirus provider when/if you ask a question on a Windows forum about this issue.

P.S. I see you posted this question on a Windows 8.1 computer. The related Microsoft KB article for Windows 8.1 is: https://support.microsoft.com/en-us/help/4056895/windows-81-update-kb4056895