Security Updates Exchange 2013-2019 (Jan2023)


The Exchange product group released January updates for Exchange Server 2013, 2016 and 2019.

The vulnerabilities addressed in these Security Updates are:

VulnerabilityCategorySeverityRating
CVE-2023-21764Elevation of PrivilegeImportantCVSS:3.1 7.8 / 6.8
CVE-2023-21763Elevation of PrivilegeImportantCVSS:3.1 7.8 / 6.8
CVE-2023-21745SpoofingImportantCVSS:3.1 8.8 / 7.9
CVE-2023-21762SpoofingImportantCVSS:3.1 8.0 / 7.0
CVE-2023-21761Information DisclosureImportantCVSS:3.1 7.5 / 6.5

The Security Updates for each Exchange Server version are linked below. Note that only CVE-2023-21762 applies to Exchange Server 2013:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.21KB5022193KB5019758
Exchange 2019 CU11Download15.2.986.37KB5022193KB5019758
Exchange 2016 CU23Download15.1.2507.17KB5022143KB5019758
Exchange 2013 CU23Download15.0.1497.45KB5022188KB5019758

In case you are wondering why Exchange Server 2016 CU22 is not mentioned: CU22 went out of support, and only CU23 will continue to receive security updates. On another note, Exchange 2013 support will end in April, 2023, meaning it it will stop receiving security updates. Recommendation is to upgrade to a more recent version.

Payload Serialization Signing
Apart from fixing security issues, these SUs also introduce support for certificate-based signing of PowerShell serialization payloads. TLDR; it allows for signing data to identify possible tampering. More info on the topic here. The process is explained at https://aka.ms/HC-SerializedDataSigning. In order to verify or configure signing, a script has been published here, or check here if you prefer manual steps. Note that all your Exchange servers need to run this SU before you enable signing, as each Exchange server needs to understand the signing.

Other Issues
Apart from security fixes, these SUs also fix the following:

Issue Ex2013Ex2016Ex2019
Store Worker Process stops and returns “System.NullReferenceExceptions” multiple times per dayYesYes
Can’t record or play in Exchange Unified MessagingYesYes
Exchange Application log is flooded with Event ID 6010Yes

Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU12 to Exchange 2019 CU11. When downloading, the security update will carry the same name for different Cumulative Updates, and I would suggest tagging the file name with the CU level when archiving it, e.g. Exchange2019-CU12-KBXXXXXX-x64-en.msp.

Exchange servers running as part of hybrid deployment are managed through PowerShell, and thus need to be receive this patch and eventually be enabled for payload signing. If you are running Exchange 2019 Management Tools-only (for recipient management), you do not need to deploy this SU.

On a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Security Updates Exchange 2013-2019 (Nov2022)


The Exchange product group released November updates for Exchange Server 2013, 2016 and 2019. Note that these Security Updates address the vulnerabilities CVE-2022-41040 and CVE-2022-41082 that were reported end of September. More on those in an earlier post.

Note: You can keep the current URLScan mitigations in-place, and remove them after installing these security updates at your convenience. The recommendation to disable Remote PowerShell for non-admins is upheld, but this is best practice regardless.

The vulnerabilities addressed in these Security Updates are:

VulnerabilityCategorySeverityRating
CVE-2022-41040Elevation of PrivilegeCriticalCVSS:3.1 8.8 / 7.9
CVE-2022-41082Elevation of PrivilegeImportantCVSS:3.1 8.8 / 8.3
CVE-2022-41078Elevation of PrivilegeImportantCVSS:3.1 8.0 / 7.0
CVE-2022-41123Elevation of PrivilegeImportantCVSS:3.1 7.8 / 6.8
CVE-2022-41079Elevation of PrivilegeImportantCVSS:3.1 8.0 / 7.0
CVE-2022-41080Elevation of PrivilegeCriticalCVSS:3.1 8.8 / 7.7

The following Security Updates address these vulnerability for the Exchange builds mentioned, with the exception of CVE-2022-41123 which does not apply to Exchange Server 2013:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.20KB5019758KB5019077
Exchange 2019 CU11Download15.2.986.36KB5019758KB5019077
Exchange 2016 CU23Download15.1.2507.16KB5019758KB5019077
Exchange 2016 CU22Download15.1.2375.37KB5019758KB5019077
Exchange 2013 CU23Download15.0.1497.44KB5019758KB5019076

In case you missed it, per the Security Updates of August, you can enable Windows Extended Protection for increased protection against certain vulnerabilities. More information this process and its requirements can be found in the post on the August updates here.

Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU12 to Exchange 2019 CU11. 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-CU12-KBXXXXXX-x64-en.msp.

Exchange servers running as part of hybrid deployment are running services, and thus need to be included in the patch cycle. If you are running Exchange 2019 CU12 Management Tools-only (for recipient management), you do not need to deploy this SU.

On a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Security Updates Exchange 2013-2019 (Oct2022)


The Exchange product group released October updates for Exchange Server 2013, 2016 and 2019. Note that these Security Updates do NOT address the vulnerabilities CVE-2022-41040 and CVE-2022-41082 that have been reported on since end of September. For now, mitigate those by follow the instructions mentioned an earlier post here.

The vulnerabilities addressed in these Security Updates are mostly the same as the ones addressed by the Security Updates of August, with the exception of CVE-2022-34692. Also, the CVSS rating of CVE-2022-30134 has been adjusted:

VulnerabilityCategorySeverityRating
CVE-2022-21979Information DisclosureImportantCVSS:3.1 4.8 / 4.2
CVE-2022-21980Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-24477Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-24516Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-30134Elevation of PrivilegeImportantCVSS:3.1 6.5 / 5.7
(was CVSS:3.1 7.6 / 6.6)

The following Security Updates address these vulnerability for the Exchange builds mentioned:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.15KB5019077KB5015322
Exchange 2019 CU11Download15.2.986.30KB5019077KB5015322
Exchange 2016 CU23Download15.1.2507.13KB5019077KB5015322
Exchange 2016 CU22Download15.1.2375.32KB5019077KB5015322
Exchange 2013 CU23Download15.0.1497.42KB5019076KB5015321

In case you missed it, per the Security Updates of August, you can enable Windows Extended Protection for increased protection against certain vulnerabilities. More information this process and its requirements can be found in the post on the August updates here.

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU12 to Exchange 2019 CU11. 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-CU12-KBXXXXXX-x64-en.msp.

Exchange servers running as part of hybrid deployment are running services, and thus need to be included in the patch cycle. If you are running Exchange 2019 CU12 Management Tools-only (for recipient management), you do not need to deploy this SU.

On a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Exchange 0-days: CVE-2022-41040 & CVE-2022-41082


Update (Oct10, 2022): Updated URL Rewrite Rule (again).

End of last week, the Exchange world was made aware of a 0-day vulnerability and exploit through the following tweet by security researcher Kevin Beaumont. The tweet referenced a write-up by GTSC Cyber Security, which published their discovery on a what looked like a variation on ProxyShell, allowing for Remote code execution. The vulnerabilities have been registered by the Common Vulnerabilities and Exposures program as CVE-2022-41040 (ZDI-CAN-18333 at Zero Day Initiative) and CVE-2022-41082 (ZDI-CAN-18802).

The 0-day impacts current versions of Exchange Server 2019, Exchange Server 2016 as well as Exchange Server 2013 when published externally. If you have Exchange Hybrid deployed only for recipient management or mail-flow (i.e. no inbound traffic for https/443), you should be OK. Similar to ProxyShell, the vulnerability consists of sending manufactured requests to Exchange server, e.g.

Read the full of this article on ENow here.

Update (Oct10): The (original) filter to mitigate the situation, as specified originally by the GTSC as well as various websites, is too specific. The filter can easily be circumvented by – but effectively identical – variations on the manufactured request. The latest rule to filter requests is:

(?=.*autodiscover)(?=.*powershell) 

Update any existing mitigation IIS URL Rewrite Rules with this Regular Expressions filter for {UrlDecode:{REQUEST_URI}} blocking (Abort Request) any matching request. When using EEMS, this rule will also be deployed in the most recent update (1.0.9). Microsoft rather silently updated the filter in their published EEMS rules during the weekend.

Microsoft added to their advisory, recommending organizations to disable Remote PowerShell for non-administrators roles (instructions here). For those wanting to hunt for indicators of compromise, check the end of the Security blog.

Vendors are also offering solutions to filter these requests using their network devices:

At the time of writing, Microsoft has not publish a security fix yet.

Security Updates Exchange 2013-2019 (Aug2022)


The Exchange product group released Augustus updates for Exchange Server 2013, 2016 and 2019.

Note that per the previous May cycle, Security Updates will be packaged in an executable wrapper. This should trigger the running elevated prompt, thus preventing any potential issues when admins simply double-click the .MSP file. More about the new package format, options for logging and command-line switches are mentioned in an article dedicated to the change of distribution method here.

Windows Extended Protection
Special attention in this cycle for Windows Extended Protection, which needs to be enabled to address certain vulnerabilities. WEP is ONLY supported for specific versions of Exchange server – see the documentation for details regarding requirements and known issues. TLDR; – list might change over time, consult the pages linked earlier:

  • Requirements
    • Supported on Exchange 2013 CU23, Exchange 2016 CU22 and Exchange Server 2019 CU11 or later, with the August 2022 Security Updates installed.
    • Cannot be enabled on Exchange Server 2013 servers hosting Public Folders in co-existence with Exchange 2016/2019.
    • Cannot be enabled on Exchange 2016 CU22 or Exchange 2019 CU11 or older hosting a Public Folder Hierarchy.
    • Does not work with hybrid servers using Modern Hybrid configuration.
    • SSL Offloading scenarios are currently not supported.
    • Consistent TLS configuration is required across all Exchange servers.
  • Known Issues
    • Retention Policies using action Move to Archive stops working.
    • In Exchange 2013, the MAPI over HTTP probe OutlookMapiHttpCtpProbe might show FAILED.

To perform prerequisite checks and implement WEP, a supporting script ExchangeExtendedProtectionManagement.ps1 has been published. Since enabling WEP impacts how clients and Exchange server communicates, it is highly recommended to test this first on your specific configuration, especially with 3rd party products, before enabling it in production.

Security Updates
So, on with the security updates. The vulnerabilities addressed in the Security Updates for August are:

VulnerabilityCategorySeverityRating
CVE-2022-21979Information DisclosureImportantCVSS:3.1 4.8 / 4.2
CVE-2022-21980Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-24477Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-24516Elevation of PrivilegeCriticalCVSS:3.1 8.0 / 7.0
CVE-2022-30134Elevation of PrivilegeImportantCVSS:3.1 7.6 / 6.6
CVE-2022-34692Information DisclosureImportantCVSS:3.1 5.3 / 4.6

The following Security Updates address this vulnerability:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.12KB5015322KB5014261
Exchange 2019 CU11Download15.2.986.29KB5015322KB5014261
Exchange 2016 CU23Download15.1.2507.12KB5015322KB5014261
Exchange 2016 CU22Download15.1.2375.31KB5015322KB5014261
Exchange 2013 CU23Download15.0.1497.40KB5015321KB5014260

These Security Updates also fix the following issues:

  • KB5017261 Start-DatabaseAvailabilityGroup fails with BlockedDeserializeTypeException
  • KB5017430 E-Discovery search fails in Exchange Online

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU12 to Exchange 2019 CU11. 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-CU12-KBXXXXXX-x64-en.msp.

Exchange servers running as part of hybrid deployment are running services, and thus need to be included in the patch cycle. If you are running Exchange 2019 CU12 Management Tools-only (for recipient management), you do not need to deploy this SU.

On a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Analyzing Exchange Online scripts


Updated: 1.2 adds default ExchangeOnlineManagement cmdlets scanning and authentication options.

Since the original announcement on deprecation of Basic Authentication, organizations had time to analyze their environment which may include Exchange-related procedures and tools. These usually also contain scripts or commands, which depend on the Exchange Online Management module. A previous blog on its history and how version 2 of this module lends itself for unattended operation with certificate-based modern authentication support can be found here.

The initial release of the Exchange Online Management v2 – or EXOv2 – module offered a an additional small set of cmdlets which utilized REST-based services. Apart from the functional discrepancies, such as having to specify a property set to indicate which properties to return, the big advantage of these added commands was that they did not depend on the Windows Remote Management (WinRM) client using Basic Authentication for token exchange. Disabling Basic Authentication on WinRM client lead to messages such as:

Connecting to remote server outlook.office365.com failed with the following error message : The WinRM client cannot process the request. Basic authentication is currently disabled in the client configuration.

This dependency makes it challenging for organizations to turn off Basic Authentication altogether, or lead to problems when they did. Fast forward to the present, where the Exchange Online Management module in its current release is offering nearly all Exchange cmdlets in REST-based form, with full functional parity.

While I expect Microsoft to reach full command parity before they flick the Basic Authentication switch to off, there are also other use cases for which analyzing scripts might be helpful:

  • Ths initial purpose was identifying commands which require RPS (Remote PowerShell), and thus thus require WinRM Basic Authentication enabled. Because the Exchange Team did an amazing job in catching up in the recent months, only few Exchange Online cmdlets are still lacking REST support in my tenant at this moment, e.g. New-ApplicationAccessPolicy. But then again, your mileage may vary, as the recent Preview 7 module removed few UnifiedGroup related cmdlets which had issues.
  • New Exchange Online commands may not receive immediate REST support.
  • Organizations might want to cross-reference commands with scripts.
  • Identifying Exchange Online commands and parameters in scripts helps in determining the minimum set of permissions required to run the script.

To analyze and report on Exchange Online scripts, I created a simple script Analyze-ExoScript.ps1. This script, which is available on GitHub here, does the following:

  • Connect to Exchange Online using RPS and inventory the commands available. Note that this requires the UseRPSSession switch when connecting, which is only available per 2.0.6-Preview3 of the module. If your organization only runs GA versions of the module, this script cannot be used.
  • Connect to Exchange Online using REST and inventory the commands available. It will re-use the account used for authenticating the RPS session, which should prevent receiving another authentication dialog or MFA challenge.
  • Cache cmdlet information in an external file to prevent having to connect to Exchange Online for every run. The file is named EXO-CmdletInfo.xml and will be stored in the same folder as the script.
  • Process the script and report on the Exchange-related commands used.

Usage
Calling Analyze-ExoScript is straightforward:

.\Analyze-ExoScript.ps1 [-File <FileName[]>] [-ShowAll] [-Refresh] [-Organization <String> -AppId <String> -CertificateFile <String> [-CertificatePassword <SecureString>] -CertificateThumbprint <String>] [-Credential <SecureString>]

Where:

  • File is the name of one or more files which you want to analyze. Note that the script accepted pipeline output, so you can also feed it filenames using Get-ChildItem for example.
  • The ShowAll switch tells the script to output all found commands, not only the Exchange ones.
  • The switch Refresh tells the script to ignore saved command information, trigger reconnecting to Exchange Online in order to refresh the command sets.
  • Credential specifies the (Basic Authentication) credential to pass to Connect-ExchangeOnline.
  • Organization and AppId can be used to specify the tenant ID (x.onmicrosoft.com) and registered application ID to use with Connect-ExchangeOnline using Modern Authentication. This also requires one of the following:
    • CertificateThumbprint of the certificate to use for authentication.
    • CertificateFile of the file containing the certificate to use, together with CertificatePassword to specify its password.

When asked to authenticate, make sure your role has the necessary Exchange-related permissions as that will determine the Exchange Online cmdlets available to you, and consequently also the commands which Analyze-ExoScript will recognize in scripts to process.

For example, to process a script Fix-MailboxFolders.ps1, use:

.\Analyze-ExoScript.ps1 -File .\Fix-MailboxFolders.ps1

The script can accept files via the pipeline. For example, to process multiple scripts use something like:

Get-ChildItem -Path C:\temp*.ps1 | Analyze-ExoScript.ps1

The output consists of objects, which allow for further filtering:

The returned properties are:

  • Command is the Exchange Online command identified
  • Type will tell you if the command supports REST or requires RPS.
  • Parameters are the parameters used together with the command. This includes common parameters, which might be less usable for role assignment purposes.
  • Alt contains alternative REST-based cmdlet you could consider using for performance reasons, e.g. Get-EXOMailbox instead of Get-Mailbox.
  • File and Line are the file containing the command and on which line it is located.

AST
To analyze code, I leveraged PowerShell feature called Abstract Syntax Tree, which was an interesting exploration in itself. PowerShell AST can be used to decompose PowerShell code into tokens. This is way better than simply looking for strings, and does away with having to interpret code yourself to see if something is a command, comment or just some string. AST allows for analysis of these tokens, in this case filtering on commands which are related to Exchange Online. If you want to get started on AST, check out this article, or plunge in the PowerShell SDK straightaway.

Final Words
When every Exchange Online command discovered is found to be offering REST support, you can turn off Basic Authentication on the client, for example through GPO or by reconfiguring WinRM:

winrm set winrm/config/client/auth @{Basic="false"}

Only thing you might need to refactor is if and how the script connects to Exchange Online, as Basic Authentication allowed for connecting to Exchange Online using (stored) credentials for example. Examples on how to use more secure Modern Authentication-based methods to connect can be found in an earlier article here.

Basic Authentication: End of an Era


1sep2022: Added announcement regarding Jan2023 extension

Back in September 2019, Microsoft announced it would start to turn off Basic Authentication for non-SMTP protocols in Exchange Online on tenants where the authentication protocol was detected as inactive. This is part of an overall movement to deprecate the less secure Basic Authentication, which is unfit to face the security challenges of the modern world, being subject to things like password spray attacks. It’s modern successor, modern authentication or OAuth2, uses a token and claim based mechanism contrary to sending accounts and passwords, and is the preferred authentication method. When combined with Azure AD for authentication, Modern Authentication also supports features such as Multi-Factor Authentication or Conditional Access.

The original date for disabling of Basic Authentication was October 13th, 2020. Then the world had other matters to deal with, and Microsoft extended the timelines. After initially postponing turning Basic Authentication off to second half of 2021, the ‘start date’ for permanently turning the lights off for Basic Authentication was set to October 1st, 2022, as per this article on Docs and MC286990 in the Message Center. Mind the ‘start’ in start date, as flicking the switch for millions of tenants takes time before it becomes effective on your tenant. Organizations do need to anticipate on this change for the first of October.

On September 1st, Microsoft published an update to these timelines as there were still some cases were organizations could not make the deadline of October 1st. To meet these customers “one last time”, organizations can now use the self-service diagnostics to extend disabling of Basic Authentication to January 2023. This needs to be done per protocol, also if organizations requested opt-out or re-enabled Basic Authentication earlier. Details as well as instructions and revised timelines on Basic Authentication switching off are laid out in a new article.

Until then, organizations can (re-)enable Basic Authentication for the protocols they need, using the self-help system in the Microsoft 365 admin center. After entering “Diag: Enable Basic Auth in EXO” in the problem search query, the request will be checked, and Basic Authentication will get enabled. But with the end of support for Basic Authentication, so will this temporary workaround. On a side note, per end of 2020, newly created tenants already have basic authentication disabled by means of security defaults – if those organizations require Basic Authentication for some reason, they will also need to reconfigure security defaults which by default is an all or nothing option for all protocols.

So, with the doomsday counter ticking away for Basic Authentication, what are the consequences for Exchange related workloads organizations might wonder. In this article, I will address some of these concerns.

Update: Microsoft meanwhile has disclosed much awaited details on changes in the native Mail app on iOS. This update is effective per iOS 15.6, and adds support for migrating configured accounts from using Basic Authentication to using Modern Authentication (OAuth). For this work work seamlessly and without user interruption, some configuration is needed on the back-end. Details can be found in a separate article here on this specific topic.

Click here to read the full article on ENow Solutions blog. Note that the ENow article does not include later updates, such as the latest timeline revisions and iOS account conversion, both mentioned above.

Security Updates Exchange 2013-2019 (Mar2022)


The Exchange PG released March updates for Exchange Server 2013, 2016 and 2019. More detailed information on patching and how to get current when running an earlier CU of Exchange, can be found at the original blog post here.

The vulnerabilities addressed in these security updates are:

VulnerabilityCategorySeverityRating
CVE-2022-23277Remote Code ExecutionCriticalCVSS:3.1 8.8 / 7.7
CVE-2022-24463SpoofingImportantCVSS:3.1 6.5 / 5.7

These vulnerabilities are addressed in the following security updates below. The exception is KB5010324 which does not fix CVE-2022-24463 for Exchange 2013. If this is because of the severity classification or the problem being non-existent for Exchange 2013, has not been not disclosed.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU11Download15.2.986.22KB5012698KB5008631
Exchange 2019 CU10Download15.2.922.27KB5012698KB5008631
Exchange 2016 CU22Download15.1.2375.24KB5012698KB5008631
Exchange 2016 CU21Download15.1.2308.27KB5012698KB5008631
Exchange 2013 CU23Download15.0.1497.33KB5010324KB5008631

Finally, KB5010324 also contains the following additional fix for Exchange 2013:

  • 5012925 RFC certificate timestamp validation in Exchange Server 2013

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU11 to Exchange 2019 CU10. 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-CU10-KBXXXXXX-x64-en.msp.

As a reminder, run the Security Update from an elevated command prompt to prevent issues during installation. In other words: Do not just double-click on the .MSP file. And on a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Security Updates Exchange 2013-2019 (Jan2022)


Another year, another Patch Tuesday! A quick blog on January 2022’s security updates for Exchange Server 2013 up to 2019.

The vulnerabilities addressed in these security updates are:

VulnerabilityCategorySeverityRating
CVE-2022-21969Remote Code ExecutionImportantCVSS:3.1 9.0 / 7.8
CVE-2022-21855Remote Code ExecutionImportantCVSS:3.1 9.0 / 7.8
CVE-2022-21846Remote Code ExecutionCriticalCVSS:3.0 9.0 / 7.8

Vulnerabilities mentioned in the table above are addressed in the following security updates.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU11Download15.2.986.15KB5008631KB5007409
Exchange 2019 CU10Download15.2.922.20KB5008631KB5007409
Exchange 2016 CU22Download15.1.2375.18KB5008631KB5007409
Exchange 2016 CU21Download15.1.2308.21KB5008631KB5007409
Exchange 2013 CU23Download15.0.1497.28KB5008631KB5007409

More detailed information can be found at the original blog post here. The security update also fixes the OWA redirection problem for Exchange hybrid deployments introduced with the November security updates.

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU11 to Exchange 2019 CU10. 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-CU10-KBXXXXXX-x64-en.msp.

As a reminder, run the Security Update from an elevated command prompt to prevent issues during installation. In other words: Do not just double-click on the .MSP file. And on a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.

Security Updates Exchange 2013-2019 (Nov2021)


Another month, another Patch Tuesday! A quick blog on November’s security updates for Exchange Server 2013 up to 2019. The vulnerabilities addressed in these security updates are:

VulnerabilityCategorySeverityRating
CVE-2021-42321Remote Code ExecutionImportantCVSS:3.1 8.8 / 7.7
CVE-2021-42305SpoofingImportantCVSS:3.1 6.5 / 5.7
CVE-2021-41349SpoofingImportantCVSS:3.1 6.5 / 5.7

Vulnerabilities mentioned in the table above are addressed in the following security updates. Exception is Exchange 2013 CU23 which seemingly only gets fixed for CVE-2021-26427; it is unclear if that is because of Exchange 2013’s lifecycle phase or because the problem does not exist in those builds.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU11Download15.2.986.14KB5007409KB5007012, KB5007011
Exchange 2019 CU10Download15.2.922.19KB5007409KB5007012, KB5007011
Exchange 2016 CU22Download15.1.2375.17KB5007409KB5007012, KB5007011
Exchange 2016 CU21Download15.1.2308.20KB5007409KB5007012, KB5007011
Exchange 2013 CU23Download15.0.1497.26KB5007409KB5007012, KB5007011

More detailed information can be found at the original blog post here. Check the KB articles for any known release notes, such as the possible cross-forest Free/Busy issue and HTTP headers containing version information.

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU11 to Exchange 2019 CU10. 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-CU10-KBXXXXXX-x64-en.msp.

As a reminder, run the Security Update from an elevated command prompt to prevent issues during installation. In other words: Do not just double-click on the .MSP file. And on a final note, as with any patch or update, I’d recommend to apply this in a test environment first, prior to implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates, and follow a more agile approach; the ratings are an indication of the urgency.