Tag Archives: Security

ADV190018: Security Updates Exchange 2013-2019 & 2010

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Ex2013 LogoUpdated Jun13: Corrected Ex2010SP3RU28 link

A quick note that an update was released for current Exchange versions as well as Exchange 2010 related to the following advisory:

  • ADV190018 Microsoft Exchange Server Defense in Depth Update

Unfortunately – or perhaps understandably – the advisory doesn’t present any more details than, ‘”Microsoft has released an update for Microsoft Exchange Server that provides enhanced security as a defense in depth measure.”.

You can download the security updates here:

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 CU’s, and you cannot apply the update for Exchange 2016 CU12 to Exchange 2016 CU11. I would suggest tagging the Cumulative Update in the file name when you store it, e.g. Exchange2016-KB4503027-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.

Turla LightNeuron: Facts from Fud

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fudYesterday, an article was published on ZDNet, where the author claims “Russian Cyberspies” are exploiting a backdoor in Exchange. The article is based on a report of Slovakian-based ESET Research, which is no stranger on the anti-virus/malware market. The report, titled “Turla LightNeuron, One email away from remote code execution”, claims the group – Turla – leverages LightNeuron to exploit Exchange Server for malicious usage, using instructions hidden in image attachments delivered through e-mail to control the backdoor. The news was quickly picked up by other media, and it didn’t take long for customers to start asking questions on the topic. Time for some fact checking.

Exchange Backdoor
The article claims the group using ‘one of the most complex backdoors’ ever spotted on an email server. While complexity is relative, it could very well be that this backdoor was indeed discovered on some improperly managed Exchange Servers in the wild.

However, the exploit leverages an installed malicious MTA (Message Transfer Agent, or Transport Agents in Exchange).  An MTA is software handling incoming and outgoing e-mail messages using the Simple Mail Transfer Protocol (SMTP). A lot of legitimate 3rd party MTAs exist for Exchange Server, for example to add disclaimers to messages or for message hygiene purposes.

This LightNeuron is the actual backdoor, so there is no backdoor in Exchange. A totally different conclusion than one could read from the article’s title, and a totally different attack vector:

  • How did this Transport Agent get installed on Exchange server in the first place?
  • How was it possible to store the DLLs required by the Transport Agents, and which are likely to get caught by AV products, on Exchange Server?
  • How was it possible to perform these tasks using administrative access, which is required to install such components in the first place?

The ESET report mentions this requirement; the ZDNET article and all other media simply omit this. Note that developing your own Transport Agent isn’t rocket science; Microsoft provides instructions on how to write your own custom Transport Agent for Exchange Server on-premises.

Hidden Instructions
Sending instructions hidden in images isn’t new. Steganography became famous to public in the last decade, where Osama Bin Laden was claimed to be embedding instructions for his followers in images posted on the internet. Little messages can also easily be embedded in the structure of an image file format, with places to store custom data or instructions.

Remote Control
As the installed malicious MTA runs under administrative permissions, it is no surprise that whoever (remotely) controls the MTA, in principle controls the Exchange Server as it runs in the context of the Exchange Trusted Subsystem.

Remote Controlled malicious code is not new; it is what drives zombie computers, and it is what made some prank tools popular in the mid-90’s, when you could prank your coworkers by opening their CD trays (anyone remember those?).

Impact
ESET claims that Turla has been leveraging LightNeuron for nearly 5 years, “which shows the tool’s advanced capabilities, being able to avoid detection for so many years”. In my opinion, this shows how many organizations have more bigger issues, such as an improperly managed mail environment.

SendMail
The report also mentions LightNeuron being ported to *NIX as well, e.g. SendMail. This shows perfectly that any communications system, when compromised, can be used for man-in-the-middle attacks. However, mentioning leaks in SendMail might not drive traffic as much as mentioning ‘Backdoor in Exchange’ for media, which is a driver when you depend on advertisements.

Detection
The article claims the hidden messages make LightNeuron hard to detect. Of course, this depends. The backdoor requires installation and presence of two malicious DLL files. Any respectable AV product should catch those. Windows Server 2016+ comes with Windows Defender, which according to its encyclopaedia should be able to detect Turla variants.

Removal
Finally, the article claims that, “removing this backdoor is quite problematic”. This is utter nonsense, as any weathered Exchange administrator should be able to install or uninstall Transport Agents as part of their skill set.

Conclusion
In summary and concluding:

  • This is not a backdoor in Exchange Server.
  • The backdoor is a malicious Transport Agent which needs to be installed on the Exchange Server
  • Installing this backdoor requires administrative permissions.
  • Well-managed Exchange environments should be OK.
  • Removal is simple, and a task any Exchange admin should be able to perform.
  • Windows Defender detects Turla variants.

And last but not least:

  • Media should do proper fact-checking as opposed to blindly copying articles.
  • Media should use titles which reflect the contents, and refrain from click-bait titles.
  • ESET is a vendor selling e-mail hygiene and security-related products, which always is a potential red flag when these kinds of reports are published.

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).