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Notes on TLS/SSL 3.0 Intolerant Servers


A number of Netscape 6.x/7.x and Mozilla users have reported that some secure sites -- typically sites featuring online transactions or online banking over the https protocol -- do not display any content at all. The connection seems terminated and a blank page is displayed. This is the main symptom of the problem when Mozilla based browsers encounter TLS/SSL 3.0 intolerant servers.


There are some number of web servers in production today which incorrectly implement the SSL 3.0 specification. This incorrect implementation causes them to reject connection attempts from clients that are compliant with the SSL 3.0 and TLS (aka SSL 3.1) specifications.

Netscape 6.x/7.x and Mozilla browsers (0.9.1 and later versions) correctly implement the TLS specification, and the users cannot utilize sites which have this problem.

More details:

The SSL 3.0 and TLS (aka SSL 3.1) specs both contain a provision -- the same provision -- for detecting "version rollback attacks". It is designed to permit a server to detect a man-in-the-middle that is altering the SSL client hello (connection) requests as they pass from the client to the server, altering them by changing the protocol version number to a lower version number. This feature was kind of meaningless until TLS (SSL 3.1) came along because there was no version higher than 3.0 from which to be rolled back. TLS is now available and used, and products that have implemented the roll-back detection incorrectly are not interoperable with TLS/SSL spec-compliant clients. Normally the servers which have this problem are not equipped to deal with the TLS protocol, but instead of rolling back to SSL 3.0 as the rollback provision provides, they terminate/drop the connection, thus resulting in most cases a blank page display.
For up-to-date information, you can read a Bugzilla bug report which keeps track of this problem with Mozilla-based browsers. See Bug 59321.

How can users avoid this problem?:

What servers are currently known to exhibit TLS/SSL 3.0 intolerant behavior?:

As of this writing, this problem has been reported for the following servers: (Wherever there is an upgraded version which fixes the problem, it is indicated by an asterisked remark in the parentheses. )

N.B. There might be servers other than those listed above which exhibit this problem. If you find such a server, please let us know through a feedback address you find on this page. We will include it in an update to this document. For up-to-date information, you can read this Bugzilla bug which keeps a list of TLS/SSL 3.0 intolerant servers.

If you're the administrator of a web site running TLS/SSL 3.0 intolerant server(s), what should you do?:

How do you know you are experiencing TLS/SSL 3.0 intolerant servers?:

Because newer versions of Netscape and Mozilla have built-in workaround for the problem servers, it is now unlikely that you will experience this problem. But if you're running Netscape 6.0/6.01/6.1 PR 1or Mozilla build (prior to 6/11/2001), you should look out for the symptom described below. You may also run this test with versions later than the older versions of Netscape 6.x or Mozilla -- just in case code changes in Netscape 6.1/Mozilla 0.9.2 or later may not catch all problem servers.

is turned ON. If so, turn it OFF.

What should you do if you find a server which has this problem on Netscape 6.0/6.01/6.1 PR 1 & Mozilla (prior to 6/11/2001) browsers or later versions of the same browsers ?: