What specific sequence of events can cause "SSL_ERROR_RX_UNEXPECTED_SERVER_HELLO" in Firefox?

Question

I have a user that was visiting a site and received the following error in FireFox:

Secure Connection Failed

An error occurred during the connection to foo.foo2.com.

SSL received an unexpected Server Hello handshake message. 

(Error code: SSL_ERROR_RX_UNEXPECTED_SERVER_HELLO) 

- The page you are trying to view cannot be shown because the authenticity of the received data could not be verified. 
- Please contact the website owners to inform them of this problem.  Alternatively, use the command found in the help menu to report this broken site.

I've confirmed that the site in question was NOT running a version of OpenSSL vulnerable to heartbleed, so that's not it.

Can someone elaborate on what else could cause this issue? Timeout reaching the server? Improper load balancing / prematurely directing the user to a different system?

I'm planning to get the web admin team involved but it would help to have a general idea of what can cause this issue.

Answer 1

The list of SSL error codes can be found in this Mozilla Webpage. It contains many error codes regarding expired/invalid/bad/wrong certificates, none of which is yours.

Yours falls into a different group, SSL_ERROR_RX_UNEXPECTED ...HELLO_REQUEST-CLIENT_HELLO-SERVER_HELLO-CERT_REQUEST, and so on (15 of them, in total). Collectively, it is said that these error messages:

... indicate that the local socket received an SSL3 handshake message from the remote peer at a time when it was inappropriate for the peer to have sent this message. For example, a server received a message from another server. This probably indicates a flaw in the remote peer's implementation.

So it is nothing to worry about. I could not gather any information as to whether this indicates sloppiness or foul play. In any case, if the pc in question can connect successfully to any other SSL site, then the fault most likely is to be placed squarely on the remote server's lap, not yours.