Tag Archives: Security

CVE-2018-8581: Exchange Vulnerability

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Ex2013 LogoUpdate Feb6: Added MSRC security advisory ADV190007 .
Update Feb13: February updates comment.

A short notice on the zero-day vulnerability in the Exchange ecosystem as reported by researcher Mollema last week. Through a man-in-the-middle setup, one can exploit the permissions Exchange has with regards to Active Directory in conjunction with NTLM as well as Exchange Web Services (EWS). This 3-stage missile allows one to elevate their privileges in Active Directory, and thus to grant themselves administrative access.

The issue was already logged at 13 november in the Microsoft Security Response Center (MSRC) as CVE-2018-8581, Microsoft Exchange Server Elevation of Privilege Vulnerability. An uptake on the public attention for the issue was generated after the Mollema article, and media like The Register started publishing about it. Meanwhile Exchange fellow Tony Redmond also wrote a short note on the issue as well.

At this moment, Microsoft is fully aware of the issue, and is actively working on resolving the issue as soon as possible. Meanwhile, the mitigation mentioned in CVE-2018-8581 can be considered, which is to remove the  DisableLoopbackCheck key from HKLM:\SYSTEM\CurrentControlSet\Control\Lsa. The effect of removing this key is that it’s no longer possible to make NTLM connections on the loopback adapter (localhost), which should be OK for Kerberos authenticated sessions as they are name-based. Again, test this as for example platforms like SharePoint will break when setting this key, but nobody runs SharePoint on the same box, so for Exchange this is a valid mitigation.

Organizations are advised not to blindly implement mitigations mentioned in Mollema’s article or elsewhere in the field, as they might not be applicable to every deployment out there, or have unforseen side-effects. Then again, organizations might already have things deployed SMB signing, in which case the exploit does not apply.

Update (Feb6): Meanwhile, Microsoft Security Response Center published an advisory (ADV190007) containing guidance on how to deal with the issue at this moment. MSRC takes the EWS Throttling Policy route to block EWS Subscriptions at the original level, which of course breaks Outlook for Mac functionality (e.g. new mail notifications as the client can no longer subscribe to receive updates), or other applications which rely on this mechanism (e.g. meeting room systems). This can be mitigated by explicitly allowing EWS subscriptions for trusted users and applications.

Update (Feb13): Today the quarterly cumulative updates for Exchange 2019/2016/2013 were released, which will remove the DisableLoopbackCheck key (when present).

Security Updates Exchange 2013, 2016 & 2019

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Ex2013 LogoUpdate 14jan: Added Exchange 2010 SP3 RU25

A quick heads-up as during my vacation Microsoft released security updates for supported releases of Exchange Server 2013, 2016 as well as Exchange Server 2019. In addition, a new Rollup was released for Exchange 2010 as well, containing one of the security updates.

The security updates patch issues as reported in the following Microsoft Common Vulnerabilities and Exposures:

  • CVE-2019-0586: Microsoft Exchange Memory Corruption Vulnerability
  • CVE-2019-0588: Microsoft Exchange Information Disclosure Vulnerability

You can download the security updates here:

Notes:

  • Exchange 2010 SP3 RU25 addresses CVE-2019-0588 only.
  • KB4471389 supersedes KB4468741 and KB4459266; KB4468742 supersedes KB4458321.

Be advised that the Security Updates for Exchange 2013 and 2016 are Cumulative Update level specific. Unfortunately, the security update carries the same name for different CU’s, and you cannot apply the update for Exchange 2016 CU10 to Exchange 2016 CU11. I would suggest tagging the Cumulative Update in the file name when you archive it, e.g. Exchange2016-KB4471389-x64-en-CU10.msp.

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

Security Updates for Exchange 2016

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Ex2013 LogoA quick heads-up as Microsoft released security update for supported releases of Exchange Server 2016.

The security updates patch issues as reported in the following Microsoft Common Vulnerabilities and Exposures:

  • CVE-2018-8604: Microsoft Exchange Server Tampering Vulnerability
    A tampering vulnerability exists when Microsoft Exchange Server fails to properly handle profile data. An attacker who successfully exploited this vulnerability could modify a targeted user’s profile data.

You can download the security updates here:

Notes:

  • KB4468741 for Exchange Server 2016 CU10 supersedes KB4459266.

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

 

Security Updates for Exchange 2016, 2013 and 2010

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Ex2013 LogoA quick heads-up as during my vacation Microsoft released security updates for supported releases of Exchange Server 2016 and 2013 as well as Exchange Server 2010.

The security updates patch issues as reported in the following Microsoft Common Vulnerabilities and Exposures:

  • CVE-2018-8302 Microsoft Exchange Memory Corruption Vulnerability
  • CVE-2018-8374 Microsoft Exchange Server Tampering Vulnerability (Exchange 2016 only)

You can download the security updates here:

Notes:

  • Be advised that Exchange 2010 SP3 Rollup 23, like recent Cumulative Updates of Exchange 2016 and 2013, requires Visual C++ Redistributable Packages for Visual Studio 2013 (download).
  • KB4340731 supersedes the previous security update KB4092041 for Exchange 2016 and Exchange 2013.

Be advised that for Exchange 2013 and 2016, Security Updates are Cumulative Update level specific. While the downloaded security updates may carry the same name, the files are different and you cannot apply the downloaded security update file for Exchange 2016 CU8 to Exchange 2016 CU9. I suggest adding some form of identification of the Cumulative Update to the file name when you archive it, e.g. Exchange2016-KB4340731-x64-en-CU10.msp.

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

Issues with July Updates of Windows

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bandaidLast Update July 19th: Corrected Update information.

About a week ago, Microsoft released the July Updates for Windows systems. Unfortunately, something must have gone wrong in quality control, because people were reporting all sorts of issues, mostly related to IIS and Exchange servers.

The issue is created at the operating system level, probably due to changes in networking as mentioned in the July update notes. Therefor, symptoms can be experienced on systems running Exchange Server 2016 or even back to Exchange Server 2007.

Some of the symptoms are:

  • The World Wide Web Publishing Service – W3SVC – won’t come up, remains in a “stopping” state, but cannot fully stop or it cannot be restarted.
  • Exchange Transport and SMTP services becomes unresponsive or stops, causing mail flow issues (Source).

The issues were serious enough to have the Exchange PG publish a notice.

Meanwhile, Microsoft has released a superseding update for Windows Server 2016, and updates for older operating systems. However, looking at the information provided with updates for older operating systems, there are fixes for the original security updates, and (previews of) Monthly Rollups for the July updates. Replacements and updates may manifest themselves in Windows Update only after installing the original – faulty – update, meaning you might have to go through more than one Windows Update cycle (and possibly reboot) for the updates to become visible and installable. This applies to the Monthly Rollups as well.

The table below contains information on the original rollups and updates, the update you need to apply, and the type of update.

Operating System Original Update Update Type Comments
Windows Server 2016 KB4338814 KB4345418 Monthly Rollup Replacement
Windows Server 2012 R2 KB4338815 KB4338831 Monthly Rollup Replacement
KB4338824 KB4345424 Security Update Update for v1
Windows Server 2012 KB4338830 KB4338816 Monthly Rollup Replacement
KB4338820 KB4345425 Security Update Update for v1
Windows Server 2008 R2 KB4338823 KB4345459 Security Update Update for v1
KB4338818 KB4338821 Monthly Rollup Replacement
Windows Server 2008 KB4295656 KB4345397 Security Update Update for v1

Finally, apart from adopting a less aggressive updating strategy, this again shows unfortunately that having a separate production environment next to your test environment is no frivolous luxury.

Security Updates for Exchange 2016, 2013 and 2010

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Ex2013 LogoA quick heads-up for those that missed it that earlier this month, as Microsoft released security updates for supported releases of Exchange Server 2016 and 2013 as well as Exchange Server 2010.

The security updates patch issues as reported in the following Microsoft Common Vulnerabilities and Exposures:

  • CVE-2018-8151 – Microsoft Exchange Memory Corruption Vulnerability
  • CVE-2018-8154 – Microsoft Exchange Memory Corruption Vulnerability
  • CVE-2018-8159 – Microsoft Exchange Elevation of Privilege Vulnerability
  • CVE-2018-8153 – Microsoft Exchange Spoofing Vulnerability
  • CVE-2018-8152 – Microsoft Exchange Server Elevation of Privilege Vulnerability

You can download the security updates here:

You may notice that Exchange 2013 Service Pack 1 is still in there, but this is because Cumulative Updates and Service Packs are on a different servicing model. Every Cumulative Update is supported for three months after the release of the next Cumulative Update; Exchange 2013 SP1 entered extended support early April, and will only receive critical updates such as this one.

Be advised that for Exchange 2013 and 2016, Security Updates are Cumulative Update level specific. While the downloaded security updates may carry the same name, the files are different and you cannot apply the downloaded security update file for Exchange 2016 CU8 to Exchange 2016 CU9. I suggest adding some form of identification of the Cumulative Update to the file name when you save it, e.g. Exchange2016-KB4092041-x64-en-CU9.msp.

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

 

Exchange 2010-2016 Security Fixes

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Ex2013 LogoMicrosoft released security updates to fix a remote code execution vulnerability in Exchange Server. The related knowledge base article is KB4018588.

More information is contained in the following Common Vulnerabilities and Exposures articles:

  • CVE-2017-8521 – Scripting Engine Memory Corruption Vulnerability
  • CVE-2017-8559 – Microsoft Exchange Cross-Site Scripting Vulnerability
  • CVE-2017-8560 – Microsoft Exchange Cross-Site Scripting Vulnerability

Depending on the lifecycle status of the product, fixes are made available either through a Rollup or as a security fix for the following product levels:

As you might notice, the security fix is made available for the N-1 builds of Exchange 2013 and Exchange 2016. This could imply the issue was addressed in the latest builds of those products. I hope to receive official confirmation on this soon.

The issue is deemed Important, which means organizations are advised to apply these updates at the earliest opportunity. However, as with any update, it is recommended to thoroughly test updates and fixes prior to deploying them in a production environment.

MS17-015: Security Fix for Exchange 2013 SP1+CU14 & 2016 CU3

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Ex2013 LogoMicrosoft published security fixes for the issue described in bulletin MS17-105. Fixes have been released for the following product levels:

You are reading it correctly: the later Cumulative Updates are not affected. Earlier builds will not receive a security fix, as support is provided up to N-2 generation builds. Reason for Exchange 2013 SP1 being in there is that Service Packs are on a different support scheme.

Note that this Rollup or security fix replaces MS16-108 (kb3184736) – you can install MS13-105 over installations containing this security fix (no need to uninstall it first).

Blocking Outlook App for iOS & Android

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imageYesterday, Microsoft announced the immediate availability the Outlook for iOS and Outlook for Android preview. These apps are the former app named Acompli, which was acquired by Microsoft in December, last year. It is unlikely that Microsoft will develop and support two similar apps, so one can assume the new Outlook app will replace the current OWA for iOS and OWA for Android (or just OWA for Devices) apps.

The app isn’t without a little controversy:

  • The app stores credentials in a cloud environment from Amazon Web Services for e-mail accounts that don’t support OAuth authorization.
  • The app makes use of a service sitting between the app and your mailbox. This service acts as a sort of proxy (hence it requires those credentials), fetching, (pre)processing and sending e-mail. In some way this is smart, as it makes the app less dependent on back-end peculiarities, using a uniform protocol to communicate with the proxy service.
  • The app does not distinguish between devices (device identities are assigned to your account, which makes sense since the app uses a service to retrieve and process your e-mail).
  • The app does not honor ActiveSync policies, like PIN requirements. While true, this app is not an ordinary Exchange ActiveSync client.

You can read more about this here and here.

In all fairness, when the app was still named Accompli, nobody cried foul. But the app is now rebranded Outlook and property of Microsoft, so it seems this made the app fair game. I hope Microsoft is working behind the scenes to make the new Outlook app enterprise-ready, and I’m sure it won’t be long before we see the app’s services move from AWS to Azure. The whole outrage in the media also seems a bit misplaced, as Connected Accounts in Exchange Online, which will retrieve e-mail from a POP or IMAP mailbox, will also store credentials ‘in the cloud’.

It is recommended to treat the app as a consumer app for now, and you may want to block the app in your organization. I have written on how to accomplish blocking or quarantining faulty iOS updates before. However, in those articles I used the reported OS version to block or quarantine devices. The Outlook app proxy service reports itself as “Outlook for iOS and Android” as device model when querying your mailbox, allowing us to use the DeviceModel parameter for matching.

The cmdlet to block or quarantine the new Outlook app in Exchange 2010, Exchange 2013 or Office 365,  is:

New-ActiveSyncDeviceAccessRule –QueryString 'Outlook for iOS and Android' –Characteristic DeviceModel –AccessLevel Block

or, to quarantine:

New-ActiveSyncDeviceAccessRule –QueryString 'Outlook for iOS and Android' –Characteristic DeviceModel –AccessLevel Quarantine

For examples of alternative blocking methods using TMG or F5, check this article. If you need to specify the user agent string, use “Outlook-iOS-Android/1.0” (or partial matching on “Outlook-iOS-Android” to block future updates of the app as well).

As goes for all mobile devices in enterprise environments, as an organization it may be better to test and aprove devices and OS versions rather than to be confronted with mobile apps with possible faulty behavior after an update or which may violate corporate security policies.

Comparing Active Directory Permissions

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Every now and then you might be required to compare Active Directory account permissions. When it concerns one or few accounts, you could do the manual side-by-side comparison using Active Directory and Computers. However, when you need to check multiple accounts this task becomes tedious.

Now you could follow the practice laid out by Exchange fellow Andy Grogan here,  generating permissions output using Quest Active Roles and comparing the textual output with a comparison utility like WinMerge or WinDiff. But you can also perform this comparison using PowerShell’s Compare-Object cmdlet, which I’ll show you here.

For this task we’re going to use the Quest AD extensions (Active Roles), which you can download here. Install these extensions on a domain-joined system where PowerShell is already installed. After installation, start the ActiveRoles Management Shell and enter the following, where IdA and IdB are the Identities of the objects you want to compare:

$a= Get-QadPermission <IdA> -Inherited -SchemaDefault
$b= Get-QadPermission <IdB> -Inherited –SchemaDefault

Now $a and $b contain the permission sets of both objects. Next, we’re going to utilize compare-object to compare these two sets. When we use Compare-Object $a $b you get the following output:

image

Not quite helpful this output but it isn’t unexpected. Since we’re comparing two object sets compare-object generates a result with objects. We can make this more readable by specifying the PassThru parameter so we can post-process these objects, like displaying certain fields using the Format-Table cmdlet, e.g.

Compare-Object $a $b -PassThru | ft SideIndicator,AccountName,Rights,Source,ApplyTo

image

Presto! The SideIndicator  is included to see in which set the attribute is contained, e.g. “<=” means the element is contained in the 1st specified (reference) object and “=>” means its is contained in the 2nd (difference) object.

If you want to include equal objects in the output as well, add the IncludeEqual parameter to the Compare-Object cmdlet.