KB2992611 Winshock Update and the Broken Cipher Suites

Last week, Microsoft released an update under KB2992611 in response to a security bulletin MS14-066 to address a flaw in SChannel reported to Microsoft. As part of KB2992611, Microsoft not only patched the flaw in SChannel but they also added four new encryption cipher suites. The suites added were as follows:

TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_128_GCM_SHA256

Although it was a nice gesture to add some new cipher suites to Windows, there was a knock on effect to installing KB2992611 and adding these new cipher suites as it appears that Google Chrome for one, possibly more browsers depending on the version you have, do not accept these ciphers and the addition would cause browsers to fail to connect to websites and causing TLS sessions to be dropped. There are also other issues although less widely reported about the installation of KB2992611 causing SQL and ODBC based data connections within applications to drop dramatically in performance.

To address the problem, Microsoft have re-released KB2992611 with KB3018238 which is a secondary update which changes the default state of these new ciphers to disabled. It’s important to note that disabling the new ciphers does not remove the fix for the vulnerability in SChannel which is addressed by the original hotfix. Some people are suggesting uninstalling KB2992611 to workaround the issue but doing this will open the SChannel vulnerability again. After hearing conversations about these updates today, there is much confusion about the situation. Microsoft have not pulled KB2992611 and replaced it with KB3018238 but they have instead added KB3018238 as a secondary update. This is in contrast to replacing the update with a version 2 release which is commonplace when there are issues with updates.

If you have already installed KB2992611, you will be offered KB3018238 via Windows Update. Installing KB3018238 will disable the four new cipher suites by default to restore compatibility however you will have the option to re-enable them if you wish via the normal means for editing and selecting cipher suites. The fix for SChannel will remain in place. If you have not yet installed KB2992611, then via Windows Update, you will see KB2992611 advertised as an update for installation but upon installation, both KB2992611 and KB3018238 will be installed and both will be listed in the View Installed Updates pane in Control Panel. In this case, you will have both the cipher suites disabled and that SChannel vulnerability patched.

If you are having issues with SQL Server or ODBC connection based applications, there is no fix for this problem currently and the solution to this is community opinion to remove the previously installed KB2992611 which appears to restore order to the force. Hopefully Microsoft will address whatever the underlying issue with SQL Server and ODBC and the interaction with this fix to SChannel in future update.

In addition to KB3018238 to fix the issues with SChannel, Microsoft yesterday released two other updates. KB3011780 has been released to address a flaw in Kerberos which effects the Key Distribution Center (KDC). This is a service which runs on Domain Controllers so this update is considered critical. Another update under KB3000850 has been released as a November 2014 Rollup Update for Windows 8.1 and Windows Server 2012 R2. This rollup includes all previously released updates for the operating systems and includes the KB2992611 but it is not clear whether it includes the original release of KB2992611 or KB2992611 and the secondary KB3018238 update.

To download KB2992611 with the secondary update KB3018238 visit http://support.microsoft.com/kb/2992611. For the Kerberos update KB3011780 visit http://support.microsoft.com/kb/3011780 and lastly, for the November 2014 Rollup Update, visit http://support.microsoft.com/kb/3000850.

richardjgreen

Richard works as a Cloud Consultant for Fordway Solution where his primary focus is to help customers understand, adopt and develop with Microsoft Azure, Office 365 and System Center. Richard Green is an IT Pro with over 15 years' of experience in all things Microsoft including System Center and Office 365. He has previously worked as a System Center consultant and as an internal solutions architect across many verticals. Outside of work, he loves motorbikes and is part of the orange army, marshaling for NGRRC, British Superbikes and MotoGP. He is also an Assistant Cub Scout Leader.