ERR_SSL_PROTOCOL_ERROR: What It Means and 9 Ways to Fix It

ERR_SSL_PROTOCOL_ERROR is an error showing that the browser can’t establish a secure (HTTPS) connection with a website. In Chrome it appears with the message “This site can’t provide a secure connection”. The problem can be on the visitor’s side (clock settings, browser cache, an extension, antivirus) or come from the SSL/TLS configuration on the site’s server.

In this guide we first list the fixes you can try as a visitor, then give a checklist for site owners and server administrators.

What Causes ERR_SSL_PROTOCOL_ERROR?

Side	Possible cause
Visitor	Wrong date/time, corrupted cache or SSL state, an extension, antivirus HTTPS scanning, proxy/VPN
Network	Filtering on a corporate or school network, faulty DNS redirection
Server	An expired or incorrectly installed certificate, a missing intermediate certificate, an unsupported TLS version, a service on port 443 that doesn’t speak HTTPS

6 Fixes for Visitors

1. Check the date and time

Certificates are valid for a specific date range. If your computer’s date is wrong, the browser treats the certificate as invalid. Set the clock to “automatic”.

2. Clear the browser cache and cookies

In Chrome, delete the cache and cookies under Settings → Privacy and security → Clear browsing data, then reopen the page.

3. Clear the SSL state (Windows)

Go to Internet Options → Content → Clear SSL state. You can find it by typing “Internet Options” in the Windows search box.

4. Disable extensions

Open the site in an incognito window. If it opens there, the problem is most likely a browser extension; turn extensions off one by one to find it.

5. Temporarily turn off antivirus, VPN or proxy

Some security software inspects HTTPS traffic, which can break the connection. Turn it off temporarily and try again. If that fixes it, disable the software’s “HTTPS scanning” setting.

6. Flush the DNS cache and try another network

Type ipconfig /flushdns in Command Prompt. If possible, open the site over mobile data to see whether the problem is specific to your network.

Checklist for Site Owners and Server Administrators

Is the certificate valid?

Check the certificate’s validity and that it matches the domain:

openssl s_client -connect yourdomain.com:443 -servername yourdomain.com

You should see “Verify return code: 0 (ok)” in the output. If it has expired, renew it. For automatic renewal in cPanel, see our installing an SSL certificate in cPanel guide.

Is the intermediate certificate (chain) missing?

If the certificate chain is incomplete, some browsers and devices reject the connection. Configure the certificate on the server as a “fullchain” (certificate + intermediate certificates).

Is port 443 serving HTTPS?

If the web server responds with plain HTTP on port 443, this error appears. Check listen 443 ssl; in Nginx or SSLEngine on in Apache.

TLS versions and cipher suites

Modern browsers use TLS 1.2 and TLS 1.3. If only old protocols (SSLv3, TLS 1.0) are enabled on your server, the connection can’t be established. Enable TLS 1.2 and 1.3.

Redirect and CDN settings

If you use a CDN such as Cloudflare, check the SSL mode. The encryption setting between the CDN and your server (e.g. “Full”) must match the certificate on the server. Make sure HTTP→HTTPS redirects don’t loop.

Similar SSL Errors

• ERR_SSL_VERSION_OR_CIPHER_MISMATCH: the browser and server can’t find a common TLS version or cipher suite.
• NET::ERR_CERT_DATE_INVALID: the certificate has expired or the device clock is wrong.
• NET::ERR_CERT_COMMON_NAME_INVALID: the certificate belongs to another domain (e.g. issued for the non-www address).

Frequently Asked Questions

If ERR_SSL_PROTOCOL_ERROR appears on only one site, whose problem is it?

If it only happens on one site and also on other devices and networks, the problem is most likely on that site’s server. If it only happens on your device, try the visitor-side fixes.

The error appears on my phone but not my computer. Why?

Older operating systems may not recognise newer root certificate authorities or TLS versions. Install your phone’s system updates and check the date/time setting.

Can a free SSL certificate cause this error?

No. Properly installed free certificates (e.g. Let’s Encrypt) provide connections as secure as paid ones. The problem isn’t the type of certificate but its installation or renewal.

Related: How to Fix the ERR_CONNECTION_RESET Error? · How to Fix the “Cannot Connect to IMAP Server” Error