Security Updates Exchange 2013-2019 (Mar2023)


The Exchange product group released March updates for Exchange Server 2013, 2016 and 2019. Be advised that the Exchange team also put out a notice for fixed vulnerability in Outlook (CVE-2023-23397), together with a supporting script to analyze mailboxes for this possible exploit (link), which is rather uncommon.

The vulnerability addressed in these Security Updates for Exchange Server is:

VulnerabilityCategorySeverityRating
CVE-2022-21978Remote Code ExecutionImportantCVSS:3.1 8.8 / 7.7

The Security Updates for each supported Exchange Server build are linked below:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.26KB5024296KB5023038
Exchange 2019 CU11Download15.2.986.42KB5024296KB5023038
Exchange 2016 CU23Download15.1.2507.23KB5024296KB5023038
Exchange 2013 CU23Download15.0.1497.48KB5024296KB5023038

Note: As mentioned last month, be advised that Exchange Server 2013 support will end in April, 2023. This means: Exchange 2013 will stop to receive security updates. Recommendation is to upgrade to a more recent version, or move to Exchange Online.

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

IssueExchange 2013Exchange 2016Exchange 2019
You can’t access Toolbox on Exchange after enabling EnableSerializationDataSigningYesYesYes
EEMS stops responding after TLS endpoint certificate updateYesYesYes
Get-App and GetAppManifests fail and return an exceptionYesYesYes
EWS does not respond and returns an exceptionYesYesYes
An exception is returned while opening a template in the Exchange ToolboxYesYesYes

Notes:

  • 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.
  • Similar to Cumulative Updates, Security Updates are cumulative and you only need to install the latest SU for your CU.
  • 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 have installed the Exchange Management Tools separately for managing your on-premises Exchange Servers, or installed it after removal of the Last Exchange Server for recipient management, it is recommended to apply the Security Update.

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 (Feb2023)


[20Feb] Added information regarding issues reported.

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

The vulnerabilities addressed in these Security Updates are:

VulnerabilityCategorySeverityRating
CVE-2023-21529Remote Code ExecutionImportantCVSS:3.1 8.8 / 7.7
CVE-2023-21706Remote Code ExecutionImportantCVSS:3.1 8.8 / 7.7
CVE-2023-21707Remote Code ExecutionImportantCVSS:3.1 8.8 / 7.7
CVE-2023-21710Remote Code ExecutionImportantCVSS:3.1 7.2 / 6.3

The Security Updates for each supported Exchange Server build are linked below:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU12Download15.2.1118.25KB5023038KB5022193
Exchange 2019 CU11Download15.2.986.41KB5023038KB5022193
Exchange 2016 CU23Download15.1.2507.21KB5023038KB5022143
Exchange 2013 CU23Download15.0.1497.47KB5023038KB5022188

Note: As mentioned last month, be advised that Exchange Server 2013 support will end in April, 2023. This means: Exchange 2013 will stop to receive security updates. Recommendation is to upgrade to a more recent version, or move to Exchange Online.

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

IssueExchange 2013Exchange 2016Exchange 2019
Export-UMPrompt fails with InvalidResponseExceptionYesYesN/A
Edge Transport service returns an “EseNtOutOfSessions” ExceptionYesYesYes
Exchange services in automatic startup mode do not start automaticallyYesYesYes
Data source returns incorrect checkpoint depthYesYesYes
Serialization fails while tried accessing Mailbox Searches in ECPYesYesYes
Transport delivery service mishandles iCAL eventsYesYesYes

Notes:

  • 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.
  • Similar to Cumulative Updates, Security Updates are cumulative and you only need to install the latest SU for your CU.
  • 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 have installed the Exchange Management Tools separately for managing your on-premises Exchange Servers, or installed it after removal of the Last Exchange Server for recipient management, it is recommended to apply the Security Update.

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.

[20Feb] Shortly after release, people reported through the comments that EWS started having issues after deploying the security update. Symptoms reported were problems with (server side) searches, add-ins not loading, and calendar operations such as scheduling or sharing taking a long time to load. Since it’s EWS having problems, applications depending on this protocol also may stop to work, such as Teams.

Meanwhile, Microsoft acknowledged an issue with the initial publication, and published workaround. If experience issues and see the event 4999 in your Eventlog:

E12IIS, c-RTL-AMD64, 15.01.2507.021, w3wp#MSExchangeServicesAppPool, M.Exchange.Diagnostics, M.E.D.ChainedSerializationBinder.EnforceBlockReason, M.E.Diagnostics.BlockedDeserializeTypeException, 437c-dumptidset, 15.01.2507.021.

follow the instructions in the following KB article link:

  1. On each Exchange server, create a registry key
    New-ItemProperty -Path HKLM:\SOFTWARE\Microsoft\ExchangeServer\v15\Diagnostics -Name 'DisableBaseTypeCheckForDeserialization' -Value 1 -Type String
  2. Create a global override setting
    New-SettingOverride -Name 'Adding learning location ClientExtensionCollectionFormatter' -Component Data -Section DeserializationBinderSettings -Parameters @('LearningLocations=ClientExtensionCollectionFormatter') -Reason 'Deserialization failed'
  3. If you cannot wait until the override configuration kicks in (may take an one hour), refresh it manually:
    • Get-ExchangeDiagnosticInfo -Process Microsoft.Exchange.Directory.TopologyService -Component VariantConfiguration -Argument Refresh
    • Restart IIS and the Windows Activation Proces on each server
      Restart-Service -Name W3SVC, WAS -Force

Be advised that event 4999 might still show up in your Eventlog, and it has been reported that this might not completely does away with the issues reported. Keep an eye on the original post and EHLO blog for any future updates.

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 (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.

Security Updates Exchange 2013-2019 (Oct2021)


Welcome to another Patch Tuesday! A quick blog on October’s security updates for Exchange Server 2013 up to 2019.

The vulnerabilities addressed in these security updates are:

VulnerabilityCategorySeverityRating
CVE-2021-26427Remote Code ExecutionImportantCVSS:3.0 9.0 / 7.8
CVE-2021-41350SpoofingImportantCVSS:3.0 6.5 / 5.7
CVE-2021-41348Elevation of PrivilegeImportantCVSS:3.0 8.0 / 7.0
CVE-2021-34453Denial of ServiceImportantCVSS:3.0 7.5 / 6.5

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 CU11Download15.2.986.9KB5007012
Exchange 2019 CU10Download15.2.922.14KB5007012
Exchange 2016 CU22Download15.1.2375.12KB5007012
Exchange 2016 CU21Download15.1.2308.15KB5007012
Exchange 2013 CU23Download15.0.1497.24KB5007011

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.

Security Updates Exchange 2013-2019 (Jul2021)


Update July 20th: Added VC++2012 requirement to tip on running MT to prepare Exchange 2013 schema separately.

Another month, another Patch Tuesday! A quick blog on the July’s security updates for Exchange Server 2013 up to 2019.

The vulnerabilities addressed in these security updates are:

VulnerabilityCategorySeverityRating
CVE-2021-31196Remote Code Execution ImportantCVSS:3.0 7.2 / 6.3
CVE-2021-34470Elevation of PrivilegeImportantCVSS:3.0 8.0 / 7.0
CVE-2021-33768Elevation of PrivilegeImportantCVSS:3.0 8.0 / 7.0
CVE-2021-31206Remote Code ExecutionImportantCVSS:3.0 7.6 / 7.1

Note:

  • When looking at the MSRC information, you will notice 3 additional CVE issues addressed for July 13th. However, as far as I can see CVE-2021-34473, CVE-2021-34523 and CVE-2021-33766 were addressed in the April 2021 and eventually the May 2021 Security Updates, which also would explain MSRC’s mention of earlier CUs, such as Exchange 2019 CU8.
  • CVE-2021-31206 was the vulnerability discovered at the Pwn2Own 2021 contest.

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

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU10Download15.2.922.13KB5004780
Exchange 2019 CU9Download15.2.858.15KB5004780
Exchange 2016 CU21Download15.1.2308.14KB5004779
Exchange 2016 CU20Download15.1.2242.12KB5004779
Exchange 2013 CU23Download15.0.1497.23KB5004778

Notes:

  • CVE-2021-33768 does not seem applicable to Exchange 2019 CU9 or Exchange 2016 CU20.
  • CVE-2021-34470 is only addressed in the security update for Exchange 2013 CU23.

More detailed information can be found at the original blog post here, which mentions some specific post-deployment instructions:

  • When running n-1 CU of Exchange 2019 (CU9) or Exchange 2016 (CU20), and you do not plan to upgrade to the latest CU yet but do wish to install this Security Update, you must also update the AD Schema using the CU10 or CU21 installation files.
  • When you are running Exchange 2013 CU23 in your organization, and no later Exchange builds are present, you need to deploy a schema update immediately after deploying the Security Update. After deploying the SU, from an elevated CMD prompt, run Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms from Exchange’s bin folder. You you need to separate the update from deploying the update, see end of article for a tip.

The blog also mentions some issues, which are identical to the ones mentioned with the May 2021 Security Updates:

  • Accounts ending in ‘$’ cannot use EMS or access the ECP.
  • Cross-forest Free/Busy might stop working resulting in 400 Bad Request (solution).
  • Running cmdlets against EMC using invoked runspace might result in no-language mode error (info).

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU9 to Exchange 2019 CU8. 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-CU9-KBXXXXXX-x64-en.msp.

On another note, after deploying the security updates Exchange will start reporting its version number in the HTTP response header.

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 acceptance 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 rating implies a form of urgency.

OWA/ECP and HMAC errors
There are reports of the Security Update breaking OWA/ECP. Symptoms are browsers displaying an HMAC error:

Server Error in '/owa' Application.

ASSERT: HMACProvider.GetCertificates:protectionCertificates.Length<1
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
    
Exception Details: Microsoft.Exchange.Diagnostics.ExAssertException: ASSERT: HMACProvider.GetCertificates:protectionCertificates.Length<1

It is likely related to “Microsoft Exchange Server Auth Certificate”, which can be expired, invalid or for other reasons not being picked up. The reported solution is renewing the “Microsoft Exchange Server Auth Certificate”. This procedure can be found here. Do note that it may take an hour for the certificate to become effective. Meanwhile, you can check the comments in the original Exchange Team post, which is lively with feedback and responses.

Exchange 2013 CU23 SU & Schema Updating
Because with Exchange 2013 CU23 schema preparation needs to occur immediately after deploying the SU on (the first) Exchange 2013 CU23 server, a tip might be that you could deploy Exchange 2013 CU23 Management Tools on a workstation, install the SU on that workstation, then run the PrepareSchema from there before deploying the SU on any Exchange 2013 CU23 server.

This might also be helpful in multi-domain organizations, or organizations where AD and Exchange are managed by different teams or require separate changes. Note that performing the schema update this way requires Visual C++ 2012 Runtime, otherwise you will run into a “Exchange Server setup didn’t complete the operation” and the ExchangeSetup.log will contain “Could not load file or assembly ‘Microsoft.Exchange.CabUtility.dll”.

Security Updates Exchange 2013-2019 (May2021)


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

These fixes address the following vulnerabilities:

VulnerabilityCategorySeverityRating
CVE-2021-31209SpoofingImportantCVSS:3.0 6.5 / 5.7
CVE-2021-31207Security Feature BypassModerateCVSS:3.0 6.6 / 5.8
CVE-2021-31198Remote Code ExecutionImportantCVSS:3.0 7.8 / 6.8
CVE-2021-31195Remote Code Execution ImportantCVSS:3.0 6.5 / 5.7

These vulnerabilities can be fixed by single security update for Exchange, which you can find below:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU9Download15.2.858.12KB5003435KB5001779
Exchange 2019 CU8Download15.2.792.15KB5003435KB5001779
Exchange 2016 CU20Download15.1.2242.10KB5003435KB5001779
Exchange 2016 CU19Download15.1.2176.14KB5003435KB5001779
Exchange 2013 CU23Download15.0.1497.18KB5003435KB5001779

More detailed information can be found at the original blog post here, which also mentions some known issues and workarounds which you might encounter after deploying these updates.

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU9 to Exchange 2019 CU8. 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-CU9-KB5003435-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation (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 acceptance 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 rating implies a form of urgency.

Security Update Exchange 2013-2019 (Apr2021)


15Apr2021: Added note about Pwn2Own vulnerabilities not being addressed by these updates.

A quick blog on April’s security updates for Exchange Server 2013 up to 2019. Details regarding these vulnerabilities are confidential, but organizations are recommended to install these updates based on their rating. With patching procedures still fresh in everyone’s memory, and every Exchange on-premises server being current after the Hafnium issues, that should not be a problem, right?

The fixes address the following Remote Code Execution vulnerabilities:

VulnerabilitySeverityRating
CVE-2021-28483CriticalCVSS:3.0 9.0 / 7.8
CVE-2021-28482HighCVSS:3.0 8.8 / 7.7
CVE-2021-28481CriticalCVSS:3.0 9.8 / 8.5
CVE-2021-28480CriticalCVSS:3.0 9.8 / 8.5

More detailed information can be found at the original blog post here. Note that the recently discovered at the Pwn2Own 2021 contest are not (yet) addressed by these updates, according to this blog by the contest organizers.

The exploit can be fixed by single security update, which you can find below.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU9Download15.2.858.10KB5001779
Exchange 2019 CU8Download15.2.792.13KB5001779
Exchange 2016 CU20Download15.1.2242.8KB5001779
Exchange 2016 CU19Download15.1.2176.12KB5001779
Exchange 2013 CU23Download15.0.1497.15KB5001779

Be advised that these security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2016 CU20 to Exchange 2016 CU19. 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-CU9-KB5001779-x64-en.msp.

Also, run the Security Update from an elevated command prompt, to prevent issues during installation (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 acceptance 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 rating implies a form of urgency.