I am suddenly getting this error connecting to localhost IIS on my development machine. It has been working fine for ages, and now suddenly has this error in Firefox:

Secure Connection Failed An error occurred during a connection to localhost. 
SSL received a record that exceeded the maximum permissible length. 
(Error code: ssl_error_rx_record_too_long)

I have googled and found no clear explanation.

In IE it says:

Internet Explorer cannot display the webpage\

In Chrome it says:

Oops! This link appears to be broken.

This error often happens when Firefox is expecting a SSL connection but instead gets an unencrypted connection. What happens when you follow this link? http://localhost:443/

I've mostly only seen this when the SSL configuration on the webserver was wrong.


I have found the solution and will put it here in case it helps anyone in the future with a similar problem:

The local self signed SSL had expired about 3 weeks ago. For the first 3 weeks it was happy to show the "certificate expired" warning. Today it decided to just die for no apparent reason (when it should still be showing the expired warning).

The solution was to add a new self signed certificate.


In my case, my antivirus was the culprit. Somehow the site was considered unsafe and it replaced the response with the 'website blocked' page of the antivirus application. This information, however, was not sent with TLS so the browser interpreted that as an SSL_ERROR_RX_RECORD_TOO_LONG (chrome and edge had similar misleading error messages, internet explorer did display the 'website blocked' page so I did get a clue what is going on. After disabling antivirus for websites, everything was ok in all browsers again)


This SSL_ERROR_RX_RECORD_TOO_LONG message from Firefox is one of the messages which comes when a misconfiguration occurs on the server side.

The main cause behind it is like the listening port is misconfigured for which you must configure it to correct one, Port 443.

Another one is that it could occur if there’s no support for adequate TLS version. To overcome this problem, you must update your SSL/TLS library. In case if there's no support for TLS 1.3 for now, at least there should be for TLS 1.2

Just go through this one of the article https://www.thesslstore.com/blog/ssl_error_rx_record_too_long/ it has given the detailed explanation of the same.

I hope it helps.

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