Office Online server – Sorry there was a problem and we can’t open this document

For a current project I am working with Exchange 2019 and for OWA we want to implement Office Online Server. I did this in the past and blogged about it (Install Office Online Server 2016) so I thought it should not be a big deal.

Installed Windows 2016, installed prerequisite software, configured an SSL certificate, installed Office Online Server and created a new Office Web Apps farm.

After testing the https://fqdn/hosting/discovery and configured the organization configuration everything must be good.

When opening an attachment in OWA I do see the OOS environment, it tries to open a document and then generates this error:

“Sorry, there was a problem and we can’t open this document. If this happens again, try opening the document in Microsoft Word.”

When opening an Excel attachment, I get the following error message:
“Unable to open the file. We couldn’t find the file you wanted. It’s possible the file was renamed, moved or deleted.”

I know Office Online Server is sensitive for SSL certificates, but this was a regular Digicert certificate. Name resolution was fine as well. But the check https://fqdn/op/generate.aspx failed as well with the following (pretty useless) error:

“Server Error. We’re sorry. An error has occurred. We’ve logged the error for the server administrator.”

Unfortunately, nothing useful in the eventlog, or in the ULS logging on the Office Web Apps server. Asked colleagues, but they had only experience with Exchange 2016 and OOS.

After two days of searching, fiddling with the server, checking .NET versions (Windows 2016 comes with a newer version of .NET then required by Office Online Server), rebuilding the Office Online Server several times I realized it might be a TLS 1.2 issue. Exchange 2019 is using TLS 1.2 only by default, whereas Exchange 2016 can use multiple versions of TLS.

So, on the Windows 2016 server with OOS, I enabled strong cryptography in .NET and disabled older versions of TLS on Windows to fix the issue.

To enable strong cryptography in the .NET Framework, add the following registry key:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft.NETFramework\v4.0.30319]
"SchUseStrongCrypto"=dword:00000001

To disabled older versions or TLS, add the following registry keys:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols]

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\PCT 1.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\PCT 1.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 2.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Server]
@="DefaultValue"
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1]
@="DefaultValue"

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
@="DefaultValue"
"Enabled"=dword:00000000

After rebooting the Office Online Server, it worked as expected.

Exchange server patching performance and windows defender

Patching an Exchange server, whether it be Windows Update, a Cumulative Update or a Security Update always takes a long time. When looking at the task manager, it is always the Antimalware Service Executable (Windows Defender Antivirus Service) that is responsible for this. It just consumes a lot of processor cycles:

To overcome this and speed up the overall performance of patching the Exchange server you can temporarily disable Windows Defender.

For Exchange 2016 running on Windows 2016 follow these steps:

Start | Settings | Update and Security | Windows Defender

For Exchange 2019 running on Windows 2019 follow these steps:

Start | Settings | Update and Security | Windows Security | Open Windows Security I Virus & Threat protection I Manage Settings

And switch Real-time protection to off as shown in the following screenshot:

Much easier is using PowerShell, just execute this command:

Set-MpPreference -DisableRealtimeMonitoring $True

When patching the Exchange server you will notice how much faster it will be. When patched and rebooted, enable Windows Defender by executing the following PowerShell command:

Set-MpPreference -DisableRealtimeMonitoring $False

You can check the status of Windows defender using one of the following commands:

Get-MpPreference | select DisableRealtimeMonitoring
Get-MpComputerStatus

Check the output for RealTimeProtectionEnabled, this should be set to True. As a sidenote, there is a lot of other interesting information when executing Get-MpComputerStatus for anti-malware.

May 2021 Exchange Server security updates

On May 11, 2021 Microsoft released new Security Updates for the following Exchange server versions:

  • Exchange Server 2013 CU23
  • Exchange Server 2016 CU19 and CU20
  • Exchange Server 2019 CU8 and CU9

The following vulnerabilities have been addressed:

VulnerabilityCategorySeverity
CVE-2021-31209SpoofingImportant
CVE-2021-31207Security Feature BypassModerate
CVE-2021-31198Remote Code Execution Important
CVE-2021-31195 Remote Code Execution Important

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.

And the downloads: