Safari can't establish a secure connection to any website

Are you running any anti - virus programs? Using a VPN?

Try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.

Isolating an issue by using another user account    

Safe Mode - About.       

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply.        Pastebin.    

Etrecheck – System Information.      

Web site version if required.  https://etrecheck.com

I have similar problem.....Safari cannot make secure connection to website for my bank or for Vanguard brokerage site. Worked fine until last few days. I can access the Ameritrade site, but not Vanguard. Have had Norton Security on this MacBook for a long time.

Cannot connect safari to my etrade account. Have been able to up to two days ago