On July 13, 2021 Microsoft has released a number of Security Updates for Exchange. Security Updates are released for:
Exchange 2013 CU23
Exchange 2016 CU20 and CU21
Exchange 2019 CU9 and CU10
Some of the issues are marked ‘critical’ (Remote Code Execution) but no evidence have been found for any exploits in the wild, but it is strongly recommended to install these Security Updates as soon as possible. The following CVE’s are addressed in these Security Updates:
As always, when installing the Security Update manually from a command prompt, use elevated privileges. If you do not, installation will succeed but under the hood things break! This is not an issue when installing using Windows Update.
Note. This Security Update has a dependency on the Schema update that came with Exchange 2016 CU21 and Exchange 2019 CU10. If you are running an older version of these CUs, please update the Schema first to the latest level. If you are still running Exchange 2013, and only Exchange 2013 at the latest level, you can install the Security Update, but you must run setup.exe /PrepareSchema from the V15\bin directory. The SU installation will install the latest schema files in the V15\bin directory which will be used by the setup application to make the schema changes. Failure to do so will result in an unprotected Exchange 2013 environment.
Personally, I am happy to see no critical and zero-day issues have been found, no immediate action on Tuesday night this time 😊. However, these are still important security updates so you must install them as soon as possible.
These Security Updates are only available for the Exchange versions mentioned above. If you are on an older version of Exchange, you must first upgrade your Exchange servers to the latest CU and then deploy these Security Updates. Security Updates are cumulative, to a Security Update contains all previous fixes for this specific Cumulative Update.
A couple of remarks:
If you are running Exchange Hybrid, even if you have all your mailboxes in Exchange Online and use the on-premises Exchange server only for management purposes, you still must deploy these Security Updates on the Hybrid Server. If you have an Exchange management server (with only the management tools installed) you do not need to install the Security Updates.
Start the Security Update from a command prompt with elevated privileges. If you do not use elevated privileges, setup will fail and leave your Exchange server in an unknown state. Known problems here are with OWA and EAC. This does not apply when installing the Security Update using Windows Update or WSUS.
When the installation of the Security Update has finished it does not ask for a reboot although this is needed, so reboot the server when finished.
There we go again…. Last week there has been some rumor going on about pwn2own 2021, some kind of security contest to find any security issues in software products and according to this statement taken from the pwn2own site, vulnerabilities were found in Exchange:
“SUCCESS – The DEVCORE team combined an authentication bypass and a local privilege escalation to complete take over the Exchange server. They earn $200,000 and 20 Master of Pwn points.”
Today Microsoft released security updates for Exchange 2013, Exchange 2016 and Exchange 2019 that addresses security vulnerability found recently. The following Remote Code Execution vulnerabilities are fixed with these updates:
At this moment no active exploits using these vulnerabilities are reported.
These vulnerabilities only concern Exchange 2013/2016/2019 on-premises. Exchange Online is not vulnerable because of its different architecture. Please remember that Exchange Online uses a different codebase.
Updates are specific for Cumulative Updates, an update for CU9 cannot be installed on CU8. The CU version is in the name of the update.
Updates are cumulative, so these updates also contain all previous updates for this CU versions.
If you are running Exchange hybrid you need to update the hybrid servers as well, even when all mailboxes are in Exchange Online.
Previous mitigation scripts like EOMT will not mitigate the April 2021 vulnerabilities.
Start the updates from a command prompt with elevated privileges. If you do not, the update can finish successfully (or report no errors) but under the hood stuff will break. When updating from Windows Update there’s no need to use elevated privileges.
Use the Exchange Server Health Checker script (available from Microsoft Github) for an inventory of your Exchange environment. The script will return if any servers are behind with Cumulative Updates and Security Updates.
On December 8, 2020 Microsoft released a number of security updates for Exchange server. Despite the fact that Exchange 2010 is out of support at all, an important security update for Exchange 2010 was released as well.