Security Update Exchange 2010-2019 (Mar2021)

Update 9Mar2021: Re-added PDF link, break-down mitigation addressing and link to Krebson article.

Another month, another set of security updates for Exchange Server 2016 and 2019, including an out-of-band update for Exchange 2013 CU23 and Exchange 2010 SP3 (Rollup 32) as well. According to the related Exchange team blog, these exploits are seen being used as part of an attack chain. The security update is critical, as the vulnerability exists on all recent versions of Exchange, and which is why updates for Exchange 2013 and 2010 were made available as well.

These fixes address the following Remote Code Execution vulnerabilities:

The exploit can be fixed by security update, or in case of Exchange 2010 SP3 by applying a Rollup, which you can find in the table below per current Exchange version.

Exchange BuildDownloadBuildArticleSupersedes
Exchange 2019 CU8Download15.2.792.10KB5000871KB4602269
Exchange 2019 CU7Download15.2.721.13KB5000871KB4602269
Exchange 2016 CU19Download15.1.2176.9KB5000871KB4602269
Exchange 2016 CU18Download15.1.2106.13KB5000871KB4602269
Exchange 2013 CU23Download15.0.1497.12KB5000871KB4593466
Exchange 2010 SP3 RU32Download14.3.513.0KB5000978

Notes:

  • You may not be prompted for a reboot, but one is required.
  • When manually installing the update use an elevated command prompt, don’t just double-click the .msp. To apply an .msp from an elevated prompt, e.g. msiexec.exe /p <Full Path to File>.
  • When you need to update to a more current Cumulative Update first, update using an elevated command prompt, e.g. setup.exe /m:upgrade /IAcceptExchangeServerLicenseTerms
  • Per product group feedback, Exchange 2010 is not vulnerable to the same attack chain as Exchange 2013/2016/2019, hence the Rollup mentioning a single CVE.
  • When running product levels earlier than the ones patched, i.e. Exchange 2016 CU17, you are at risk. There are no patches for earlier product levels, so you need to update to a recent CU after which you can install the security update.
  • When installing a recent CU first in order to be able to install the security update, reboot after installing the CU, then install the security update. This prevents issues caused by files being locked or updating files pending replacement during reboot.
  • When you are significantly behind regarding keeping your Exchange servers up to date, the blog Upgrade Paths for CU’s and .NET might help in determining an update strategy.
  • The statement to stay up to date with at most CU n-1 is not some random adage; apart from features and fixes, it also allows you to quickly respond to these type of emergencies.
  • Make sure you have configured proper Anti-Virus/Malware exclusions for Exchange server, as documented here for Exchange 2016/2019. I’ve seen significant delays or even hangs during setup of Cumulative Updates because of paths and processes not being excluded. When running Exchange virtually, any I/O inspection running on top of your hypervisor is also considered anti-virus/malware software, such as Trend Micro Deep Inspection on VMWare.
  • When deploying CU(n) on top of CU(n-1) when an interim update already has been installed, it is recommended to uninstall the IU prior to deploying CU(n). While it might go through, an abort is likely with mention of detecting an IU (INTERIMUPDATEDETECTED) in Exchange Setup log.
  • Security Updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU18 to Exchange 2016 CU19. Note that the security update file has the same name for different Cumulative Updates; I would suggest tagging the file name with the CU level, e.g. Exchange2016-CU18-KB5000871-x64-en.msp.

You may want to look for signs that your Exchange server might have been compromised (Indicators of Compromise or IOC). The article HAFNIUM targeting Exchange Servers with 0-day exploits explains this process.

Microsoft also published an official communication to support this update, including steps to remediate issues with updates and steps to perform analysis (many people overlook the recommendation to run the update elevated for some reason). This deck can be found here: March 2021 Exchange Server Security Update – v1.2.65 – EN.pdf (thanks Chris Lehr).

I would also recommend the official follow-up post, which not only has been updated since the original post, but also includes mitigations for organizations which cannot deploy the update yet:

  • A script to configure IIS rewrite rules to block cookies used in the attack (mitigates CVE-2021-26855).
  • Disabling UM Services (mitigates CVE-2021-26857).
  • Disabling ECP application pool (mitigates CVE-2021-27065).
  • Disabling OAB application pool (addresses CVE-2021-26858).

Needless to say, steps like disabling ECP or OAB impacts client functionality. The post also contains a reference to the MS Emergency Response Tool which you can run to detect and remediate vulnerabilities on systems which are not covered by Defender.

Since some people are discovering artifacts of HAFNIUM dating before Microsoft’s official communication, people have been wondering how long this has been going on. For those interested, Krebson Security has published an article with a concise timeline of the events related to this attack. Reports are an estimated 10,000 to over 30,000 Exchange on-premises servers have been hit.

Security Recommendation Exchange 2016-2019

A quick blog on an updated security publication for Exchange Server 2016 and 2019. This publication addresses the following vulnerability:

CVE-2021-1730: Microsoft Exchange Server Spoofing Vulnerability

A spoofing vulnerability exists in Microsoft Exchange Server which could result in an attack that would allow a malicious actor to impersonate the user.

As mentioned in the CVE report, this vulnerability can be mitigated in Exchange 2016 and Exchange 2019 by implementing a separate namespace for inline images. These images are served when using Outlook Web Access. Since I never see customers implementing this option, I will repeat these steps below to bring this to your attention.

First, pick a namespace to serve these images from, e.g. img.mail.contoso.com. Create a CNAME for this entry in the DNS, and point it to your OWA namespace, for example img.mail.contoso.com. Add this namespace to your existing SSL certificate (SAN) unless you are using a wildcard certificate and the chosen namespace is covered by it.

Next, configure the InternalDownloadHostName and ExternalDownloadHostName properties from OWAVirtualDirectory configuration, e.g.

Get-OwaVirtualDirectory | Set-OwaVirtualDirectory -ExternalDownloadHostName img.mail.contoso.com -InternalDownloadHostName img.mail.contoso.com

Configure the Exchange organization to use download domains:

Set-OrganizationConfig -EnableDownloadDomains $true

Finally, restart IIS or recycle the OWA application pool using Restart-WebAppPool MSExchangeOWAAppPool.

Security Update Exchange 2016-2019 (Feb2021)

A quick blog on security updates for Exchange Server 2016 and 2019. These fixes address the following vulnerability:

CVE-2021-24085: Microsoft Exchange Server Spoofing Vulnerability

The exploit can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU8Download15.2.792.5KB4602269KB4593465
Exchange 2019 CU7Download15.2.721.8KB4602269KB4593465
Exchange 2016 CU19Download15.1.2176.4KB4602269KB4593465
Exchange 2016 CU18Download15.1.2106.8KB4602269KB4593465

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU17 to Exchange 2016 CU16. Also, the security update download has the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level, e.g. Exchange2019-CU6-KB4588741-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation. And on a final note, as with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Security Updates Exchange 2010-2019 (Dec2020)

A quick blog on security updates for Exchange Server 2013, 2016 and 2019 released December 8th. These fixes address the following vulnerability:

Exchange 2016 / 2019

  • CVE-2020-17117: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17132: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17141: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17142: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17143: Microsoft Exchange Information Disclosure Vulnerability

Exchange 2013

  • CVE-2020-17117: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17132: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17142: Microsoft Exchange Remote Code Execution Vulnerability
  • CVE-2020-17143: Microsoft Exchange Information Disclosure Vulnerability

Exchange 2010

  • CVE-2020-17144: Microsoft Exchange Remote Code Execution Vulnerability

The exploits can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU7Download15.2.721.6KB4593465KB4588741
Exchange 2019 CU6Download15.2.659.11KB4593465KB4588741
Exchange 2016 CU18Download15.1.2106.6KB4593465KB4588741
Exchange 2016 CU17Download15.1.2044.12KB4593465KB4588741
Exchange 2013 CU23Download15.0.1497.10KB4593466
Exchange 2010 SP3 RU31 Download14.3.509.0KB4593467

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU17 to Exchange 2016 CU16. Also, the security update download has the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level, e.g. Exchange2019-CU6-KB4588741-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation. And on a final note, as with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Security Updates Exchange 2013-2019 (Nov2020)

A quick blog on security updates for Exchange Server 2013, 2016 and 2019 released November 10th. These fixes address the following vulnerability:

  • CVE-2020-17085: Microsoft Exchange Server Denial of Service Vulnerability
  • CVE-2020-17084: Microsoft Exchange Server Remote Code Execution Vulnerability
  • CVE-2020-17083: Microsoft Exchange Server Remote Code Execution Vulnerability

The exploits can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU7Download15.2.721.4KB4588741KB4581424
Exchange 2019 CU6Download15.2.659.8KB4588741KB4581424
Exchange 2016 CU18Download15.1.2106.4KB4588741KB4581424
Exchange 2016 CU17Download15.1.2044.8KB4588741KB4581424
Exchange 2013 CU23Download15.0.1497.8KB4588741KB4581424

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU17 to Exchange 2016 CU16. Also, the security update download has the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level, e.g. Exchange2019-CU6-KB4588741-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation. And on a final note, as with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Security Updates Exchange 2016-2019 (Sep2020)

A quick blog on security updates for Exchange Server 2016 and Exchange Server 2019 released September 8th. These fixes address the following vulnerability:

  • CVE-2020-16875: Exchange Memory Corruption Vulnerability
    A remote code execution vulnerability exists in Microsoft Exchange server due to improper validation of cmdlet arguments. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the System user. Exploitation of the vulnerability requires an authenticated user in a certain Exchange role to be compromised. The security update addresses the vulnerability by correcting how Microsoft Exchange handles cmdlet arguments.

The exploits can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU6Download15.2.659.6KB4577352KB4540123
Exchange 2019 CU5Download15.2.595.6KB4577352KB4540123
Exchange 2016 CU17Download15.1.2044.6KB4577352KB4540123
Exchange 2016 CU16Download15.1.1979.6KB4577352KB4540123

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU17 to Exchange 2016 CU16. Also, the security update download has the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level, e.g. Exchange2016-CU17-KB4577352-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation. And on a final note, as with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Configuring Exchange Online with IMAP & OAuth2

Update 22feb2021: Added note about enabling SMTP Authentication.

Not too long ago, the Exchange product group enabled Modern Authentication (or OAuth2) support for IMAP and SMTP in Exchange Online, and shortly after for POP3 as well. This support was much needed with the imminent deactivation of Basic Authentication. With Modern Authentication available, vendors, developers as well as organizations running custom scripts are given time to adopt Modern Authentication where applicable.

By delaying the original end date of Basic Authentication from October 13, 2020 to Q3’ish 2021 due to the Corona situation, the adoption period is increased significantly. That does not mean however developers and organizations can sit back and relax: Act sooner rather than later, the end of Basic Authentication is nigh.

The benefits of Modern Authentication are of course that it is a more secure model (e.g. resistant to password spray attacks), as well that it can leverage Microsoft 365 functionality like Conditional Access to limit protocols to certain locations.

That said, in this article I will show you how to approve usage of a popular 3rd party e-mail application Thunderbird, using IMAP protocol in conjunction with the Modern Authentication scheme. The procedures below have been run against Thunderbird 78.0b4 on Windows as well as Ubuntu.

Third Party Applications
Before we move on to Thunderbird, we first make sure the organization settings allow for third party applications to access your mailbox Exchange Online. This process has been blogged about for common popular applications, such as the native iOS Mail app or the Gmail app on Android. So, how to go ahead if your organization restricts access to third party applications, and they only want to allow specific applications, which is of course good practice.

The easiest way to add Thunderbird to the allowed applications and grant consent to the organization, is by constructing an admin consent URL. To construct the consent URL, take the following URL:

https://login.microsoftonline.com/<TenantID>/oauth2/authorize?client_id=<AppID>&response_type=code&prompt=admin_consent

and,

  1. Replace <TenantID> with your Tenant ID. This piece of information can be found under the Azure Active Directory blade in the Azure portal.
  2. Replace <AppID> with the Application ID (sometimes also referred to as Client ID) of the application you want to provide consent for. As we can see in the table below, the ID of Thunderbird is 08162f7c-0fd2-4200-a84a-f25a4db0b584.
ApplicationID
Thunderbird08162f7c-0fd2-4200-a84a-f25a4db0b584
Gmail app2cee05de-2b8f-45a2-8289-2a06ca32c4c8
iOS Accounts (Apple Mail app)f8d98a96-0999-43f5-8af3-69971c7bb423

Open your browser, and visit this URL as an administrator. You will be greeted with a consent form, in which you will be asked to accept for your organization. Because the redirect_uri is empty here, you will likely be send to a non-existing location after giving consent, but that’s OK.

When you look at the Enterprise Applications blade in the Azure Portal, you will notice the Thunderbird app has been added. Here you can further customize it, like any enterprise application supporting Modern Authentication, e.g.

  • Restrict access to specific users or groups.
  • Use Conditional Access to restrict access to certain locations.
clip_image001

Another thing to note is that permissions for Thunderbird app will have been translated to the following Graph permissions:

APIPermissionType
Microsoft GraphRead and write access to mailboxes via IMAP.Delegated
Microsoft GraphRead and write access to mailboxes via POP.Delegated
Microsoft GraphRead and write access to mailboxes via SMTP AUTH.Delegated
Microsoft GraphSign in and read user profile.Delegated

We should now be ready on the back-end.

Thunderbird
Now as an end user, start Thunderbird. Do not start configuring the account yet, as we first need to modify a Thunderbird setting to allow for successful Modern Authentication through a browser popup. Click the ‘hamburger’ menu to open the Options window. Scroll all the way down, and open the Config Editor. Click ‘I Accept the risk’. In the settings overview, set General.UserAgent.CompatMode.Firefox setting to True:

Preference NameStatusTypeValue
general.useragent.compatMode.firefoxmodifiedbooleanTrue

Close the Config Editor and Preferences tab. We can now set up our account in Thunderbird.

Select Add Mail Account, and enter your name and e-mail address. You can leave the password empty, as we will be using an Oauth token which we will retrieve later on. Press Continue to have Thunderbird figure out where your mailbox is hosted. When it properly discovers the mailbox location, it will set the configuration as follows:

image

If Thunderbird can’t figure out your settings (for some reason the Windows build could, but the Ubuntu build couldn’t), configure them as indicated above. We can’t select OAuth2 for authentication here, so leave Authentication as is; we will correct this right after we click Done.

Note: Configure manually would be the place you expect to set authentication to OAuth2 straight away, but with the build we used, the OAuth2 option is not available from the manual account setup dialog. Therefore, we need to set up the account and correct settings afterwards.

  1. In the Server Settings window related to your account, select OAuth2 authentication:
    clip_image001[14]
  2. In the Outgoing Server (SMTP) settings, select Offic365 (Microsoft) – smtp.office365.com, click Edit and set authentication for outbound SMTP to OAuth2 as well.
    clip_image002
    Note: The Thunderbird build running on Ubuntu doesn’t provide the OAuth2 authentication option for SMTP.

When finished, click ‘Get Messages’. The familiar Microsoft 365 authentication browser dialog should show up. After signing in, the next question will be to grant consent to the Thunderbird application to it can access your mailbox data and send e-mail:

clip_image001[18]

Note that this dialog can not be suppressed, as currently only interactive applications are supported. If you are working on an app or script which needs unattended access, please use Graph API.

After the user provides consent, Thunderbird is ready and will start fetching your default folders and mail items. If you want to view additional folders, you need to subscribe to them by right-clicking the account and picking Subscribe. Only folders with mail-items are supported, despite you can select every folder in your mailbox including Calendar or Contacts.

Note: If you encounter problems sending messages, please check the CASMailbox setting SmtpClientAuthenticationDisabled. If it is set to $true, you need to disable it to enable SMTP authentication, e.g.

Set-CASMailbox -Identity michel@contoso.com -SmtpClientAuthenticationDisabled $false

Logging
If you have people in your organization requiring some form of proof that Modern Authentication is being used, you can use the Enterprise Applications / Sign-Ins view from the Azure Active Directory portal.

Alternatively, you can use Thunderbird’s built-in logging capabilities. To accomplish the latter, set the following environment variables before starting Thunderbird:

MOZ_LOG=IMAP:5,timestamp
MOZ_LOG_FILE=%APPDATA%\ThunderBird-imap.log

In the generated ThunderBird-imap.log file like shown below, you should be able to spot Modern Authentication (XOAuth2) being selected:

2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: I/IMAP 259C3800:outlook.office365.com:NA:CreateNewLineFromSocket: * CAPABILITY IMAP4 IMAP4rev1 AUTH=PLAIN AUTH=XOAUTH2 SASL-IR UIDPLUS MOVE ID UNSELECT CHILDREN IDLE NAMESPACE LITERAL+2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP ReadNextLine [stream=1991DE80 nb=28 needmore=0]
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: I/IMAP 259C3800:outlook.office365.com:NA:CreateNewLineFromSocket: 1 OK CAPABILITY completed.
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP Try to log in
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP IMAP auth: server caps 0x840087635, pref 0x800000000, failed 0x0, avail caps 0x800000000
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP (GSSAPI = 0x1000000, CRAM = 0x20000, NTLM = 0x100000, MSN = 0x200000, PLAIN = 0x1000, LOGIN = 0x2, old-style IMAP login = 0x4, auth external IMAP login = 0x20000000, OAUTH2 = 0x800000000)
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP Trying auth method 0x800000000
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP IMAP: trying auth method 0x800000000
2020-06-30 13:10:16.726000 UTC - [(null) 15696: IMAP]: D/IMAP XOAUTH2 auth
2020-06-30 13:10:16.775000 UTC - [(null) 15696: IMAP]: D/IMAP ReadNextLine [stream=280D87C0 nb=180 needmore=0] 2020-06-30 13:10:16.775000 UTC - [(null) 15696: IMAP]: I/IMAP 2089A000:outlook.office365.com:NA:CreateNewLineFromSocket: * OK The Microsoft Exchange IMAP4 service is ready. [QQBNADQAUABSADAAMQAwADEAQwBBADAAMAA3ADYALgBlAHUAcgBwAHIAZAAwADEALgBwAHIAbwBkAC4AZQB4AGMAaABhAG4AZwBlAGwAYQBiAHMALgBjAG8AbQA=]

Security Updates Exchange 2010-2019 (Feb2020)

A quick blog on recently published security updates for Exchange Server 2013 up to Exchange Server 2019 and Exchange Server 2010 as well. These fixes address the following vulnerabilities:

  • CVE-2020-0692: Microsoft Exchange Server Elevation of Privilege Vulnerability

An elevation of privilege vulnerability exists in Microsoft Exchange Server. An attacker who successfully exploited this vulnerability could gain the same rights as any other user of the Exchange server. This could allow the attacker to perform activities such as accessing the mailboxes of other users. Exploitation of this vulnerability requires Exchange Web Services (EWS) to be enabled and in use in an affected environment. To exploit the vulnerability, an attacker would need to change parameters in the Security Access Token and forward it to a Microsoft Exchange Server, thereby allowing impersonation of another Exchange user. To address this vulnerability, Microsoft has changed the way EWS handles these tokens.
This vulnerability does not apply to Exchange 2010.

  • CVE-2020-0688: Microsoft Exchange Memory Corruption Vulnerability

A remote code execution vulnerability exists in Microsoft Exchange Server when the server fails to properly create unique keys at install time. Knowledge of a the validation key allows an authenticated user with a mailbox to pass arbitrary objects to be deserialized by the web application, which runs as SYSTEM. The security update addresses the vulnerability by correcting how Microsoft Exchange creates the keys during install.

The CVE documents contain more details on the vulnerabilities. In addition, KB4536989 (Rollup 30) for Exchange 2010 and KB4536988 for Exchange 2013 also fixes the following issue:

  • KB4540267 MSExchangeDelivery.exe or EdgeTransport.exe crashes in Exchange Server 2013 and Exchange Server 2010

The exploits can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU4Download15.2.529.8KB4536987KB4523171
Exchange 2019 CU3Download15.2.464.11KB4536987KB4523171
Exchange 2016 CU15Download15.1.1913.7KB4536987KB4523171
Exchange 2016 CU14Download15.1.1847.7KB4536987KB4523171
Exchange 2013 CU23Download15.0.1497.6KB4536988KB4523171
Exchange 2010 SP3 RU30KB4536989KB4509410

Be advised that the Security Updates for Exchange 2013-2019 are Cumulative Update level specific. Unfortunately, the security update carries the same name for different CUs, and you cannot apply the update for Exchange 2016 CU15 to Exchange 2016 CU14. I would suggest tagging the Cumulative Update in the file name used, e.g. Exchange2016-CU15-KB4536987-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation. And on a final note, as with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Security Updates Exchange 2013-2019 (Nov2019)

Exchange2019LogoA quick blog on recently published security updates for Exchange Server 2013 up to Exchange Server 2019. These fixes address the following vulnerabilities:

  • CVE-2019-1373: Microsoft Exchange Remote Code Execution Vulnerability

The CVE documents contain more details on the vulnerabilities. The exploits can be fixed by single security update, which you can find in the table below per current Exchange version.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU3Download15.2.464.7 KB4523171KB4515832
Exchange 2019 CU2Download15.2.397.9 KB4523171 KB4515832
Exchange 2016 CU14Download15.1.1847.5 KB4523171 KB4515832
Exchange 2016 CU13Download15.1.1779.7 KB4523171 KB4515832
Exchange 2013 CU23Download15.0.1497.4 KB4523171 KB4509409

Be advised that the Security Updates for Exchange 2013-2019 are Cumulative Update level specific. Unfortunately, the security update carries the same name for different CUs, and you cannot apply the update for Exchange 2016 CU14 to Exchange 2016 CU13. I would suggest tagging the Cumulative Update in the file name when you store it, e.g. Exchange2016-CU14-KB4523171-x64-en.msp.

As with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.

Security Updates Exchange 2016 & 2019 (Sep2019)

Today, Microsoft published security fixes for Exchange Server 2016 and 2019. These fixes address the following vulnerabilities:

The CVE documents contain more details on the vulnerabilities. These exploits can be fixed by single security updates; you can download them here:

VersionLinksBuildKB
2019 CU2Download15.2.397.6KB4515832
2019 CU1Download15.2.330.10KB4515832
2016 CU13Download15.1.1779.5KB4515832
2016 CU12Download15.1.1713.9KB4515832

Note: KB4515832 supersedes KB4509409 and KB4509408.

Be advised that these Security Updates are Cumulative Update level specific. Unfortunately, the security update carries the same name for different CU’s, and you cannot apply the same update for Exchange 2016 CU13 to Exchange 2016 CU12. I would suggest tagging the Cumulative Update in the file name when you store it, e.g. Exchange2016-KB4515832-x64-en_CU11.msp.

As with any patch or update, I’d recommend to apply this in a acceptance environment first, prior to implementing it in production.