Swedish Windows Security User Group

We have recently expanded the integration of Antimalware Scan Interface (AMSI) with Office 365 to include the runtime scanning of Excel 4.0 (XLM) macros, to help antivirus solutions tackle the increase in attacks that use malicious XLM macros. This integration, an example of the many security features released for Microsoft 365 Apps on a regular basis, reflects our commitment to continuously increase protection for Microsoft 365 customers against the latest threats.

Microsoft Defender Antivirus is using this integration to detect and block XLM-based malware, and we encourage other antivirus products to use this open interface to gain better visibility and improve protections against these threats.

XLM macros is a legacy macro language that was made available to Microsoft Excel in 1992, prior to the introduction of Visual Basic for Applications (VBA) in 1993. While more rudimentary than VBA, XLM is powerful enough to provide interoperability with the operating system, and many organizations and users continue to use its functionality for legitimate purposes. Cybercriminals know this, and they have been abusing XLM macros, increasingly more frequently, to call Win32 APIs and run shell commands.

The AMSI instrumentation for VBA has been providing deep visibility into the runtime behavior of VBA macros. Its release in 2018 effectively removed the armor that macro-obfuscation equipped malware with, exposing malicious code to improved levels of scrutiny. Naturally, threat actors like those behind Trickbot, Zloader, and Ursnif have looked elsewhere for features to abuse and operate under the radar of security solutions, and they found a suitable alternative in XLM.

Like VBA and many other scripting languages abused by malware, XLM code can be obfuscated relatively easily to conceal the real intent of the macro. For example, attackers can hide URLs or file names of executable files from static inspection through simple strings manipulations. Attackers also take advantage of the way macro code persists within the Excel document—while VBA macros are stored in a dedicated OLE stream (and hence can be easily located and extracted), XLM macros do not exist as a separate, well-defined entity. Rather, each XLM macro statement is a formula within a cell. Extracting a whole XLM macro can become a cumbersome task, requiring a cell-by-cell inspection of the whole document.

Figure 1. Sample malicious XLM macro

In addition, while formulas are typically executed downwards starting from the top, with XLM the macro content can be quite spread out, thanks to control flow statements like RUN, CALL, or GOTO, which allow the switching of execution flow from one column to another. This feature, together with obfuscation, has been abused by attackers to craft documents that could evade static analysis.

AMSI instrumentation for Excel 4.0 (XLM) macros

AMSI is an open interface that allows any application to request the scanning of any data at any time. In a nutshell, this technology provides applications the capability to interface with the installed antivirus solution in order to inspect and scan potentially dangerous data (e.g., a file downloaded from a remote location, or data generated dynamically by an application). Microsoft already utilizes this technology in various applications to detect malicious macros, script-based malware, and other threats:

• Office VBA macros
• JScript
• VBScript
• PowerShell
• WMI
• Dynamically loaded .NET assemblies
• MSHTA/Jscript9

The data provided by AMSI is leveraged extensively by Microsoft Defender for Endpoint. It provides important data for machine learning models that process billions of signals every day to identify and block malicious behaviors. The XLM instrumentation is similar to the implementation in VBA and other scripting engines that integrate with AMSI:

Figure 2. AMSI instrumentation for XLM

The XLM language allows a user to write programs that call native runtime functions, as well as external Win32 APIs. In both cases, the interfaces that dispatch the calls to these functions are intercepted and directed to an internal logger. The logger component stores the intercepted functions in text format within a circular buffer. When certain dangerous functions are called, for example the runtime function EXEC or the Win32 API ShellExecute, XLM halts the macro execution and invokes AMSI to request a synchronous scan of the circular buffer containing the functions logged up to that point. Such dangerous functions are called “trigger functions”. If the antivirus identifies the macro as malware, the execution of the macro is aborted and Excel is safely terminated, blocking the attack and preventing the malicious macro from doing any damage. Otherwise, the user experience continues seamlessly.

It’s important to observe that the interception of XLM function calls happens at runtime. This means that the logger component always registers the true behavior of all functions and associated parameters, which may contain URLs, file names, and other important IOCs, regardless of the obfuscation used by the malware.

The following is an example of an XLM macro found in a malicious document:

Figure 3. Sample XLM macro

This malicious macro consists of a series of commands (e.g., RUN, REGISTER, IF, etc.) with related parameters specified by references to other cells. For example, the token $CA$1889 passed to the first function RUN indicates that the string provided as parameter for this function is in the cell at column CA and row 1889.

This is only one of the many ways that XLM-based malware can obfuscate code. Detecting this macro is challenging because it doesn’t expose any suspicious strings or behavior. This is where the power of AMSI comes into play: the instrumentation allows XLM to inspect functions when they are invoked, so that all their parameters have already been de-obfuscated. As a result, the above macro produces a log that looks like the following:

Figure 4. Sample log

The XLM engine determines that the dangerous function ShellExecuteA is being invoked, and subsequently places the macro execution on hold and passes the macro behavioral log to AMSI for scanning. The antivirus now has visibility into a behavioral log that completely exposes all of the data including, API names, URLs, and file names. The log makes it easy to conclude that this macro is trying to download and execute a DLL payload via the tool Rundll32.

Case study: ZLoader campaign

ZLoader is a malware family that has been actively perpetrating financial theft for several years. Like many of its peers, ZLoader operates via aggressive campaigns that rely on social engineering and the abuse of Office documents spread via email.

We have been monitoring the activity of this threat and observed that in the last year the attackers shifted to XLM as their infection vector of choice. The Excel documents have a typical lure message to trick the user into clicking “Enable Content” to allow the macro code to run.

Figure 5. Malicious Excel file used in Zloader campaign

A closer look at the document reveals an Excel sheet with an obscure-looking name. That sheet embeds XLM macro formulas, which are stored several rows down to make the sheet look empty. Furthermore, the macro formulas are spread out and obfuscated, hindering static analysis and raising more challenges for identifying intent.

Figure 6. Malicious XLM macro used in ZLoader campaign

Executing and debugging the macro with Excel is not very straightforward either. The macro has long loops that are used to decode and run further obfuscated macro formulas, and the Excel’s debugger doesn’t have the ability to control the execution in a granular way in order to skip loops and break on specific formulas.

However, when this macro runs with the AMSI instrumentation enabled, it produces up to three different logs that are passed to AMSI. The first two look like the following:

Figure 7. Log produced when ZLoader’s XLM macro is run

The image only shows the final part of the log where the interesting activity shows up. We can see that the macro is issuing a new EXEC statement to run a .vbs file via explorer.exe. This EXEC statement causes the execution of the VBScript named EW2H.vbs, which has been decoded and saved to disk by the macro prior to the EXEC line. The VBScript then tries to download and run a binary payload. The macro attempts to do this twice, hence this log (with minor variations) is passed to AMSI twice.

If the above steps fail, the macro resorts to downloading the payload directly, producing the following log for AMSI:

Figure 8. Log produced when ZLoader’s XLM macro is run

The macro defines two URLs, then downloads their content with the API URLDownloadToFileA, and finally invokes the API ShellExecuteA to launch the downloaded payload (the file jxi09.txt) via rundll32.exe. We can infer from this line that the payload is a DLL.

All three logs offer plenty of opportunities to detect malicious behavior and also allow the easy extraction of relevant IOCs like URLs, file names, etc. The initial XLM code in the Excel document is completely obfuscated and contains no usable information, making it tricky to issue static detections that are both effective and durable. With the dynamic nature of AMSI, the runtime behavior can be observed in cleartext, even with obfuscation. Detections based on the logs passed to AMSI also have the advantage of being more robust and generic in nature.

Availability

Runtime inspection of XLM macros is now available in Microsoft Excel and can be used by antivirus solutions like Microsoft Defender Antivirus that are registered as an AMSI provider on the device. This feature is included as an addition to the existing AMSI integration with Office. It’s enabled by default on the February Current Channel and Monthly Enterprise Channel for Microsoft 365 subscription users.

In its default configuration, XLM macros are scanned at runtime via AMSI, except in the following scenarios:

• Files opened while macro security settings are set to “Enable all macros”
• Files opened from a trusted location
• Files that are trusted documents

Administrators can now use the existing Microsoft 365 applications policy control to configure when both XLM and VBA macros are scanned at runtime via AMSI. Get the latest group policy template files.

 

Group Policy setting name	Macro Runtime Scan Scope
Path	User Configuration > Administrative templates > Microsoft Office 2016 > Security Settings
	This policy setting specifies the behavior for both the VBA and Excel 4.0 (XLM) runtime scan features. Multiple Office apps support VBA macros, but XLM macros are only supported by Excel. Macros can only be scanned if the antivirus software registers as an Antimalware Scan Interface (AMSI) provider on the device. If you enable this policy setting, you can choose from the following options to determine the macro runtime scanning behavior: Disable for all files (not recommended): If you choose this option, no runtime scanning of enabled macros will be performed. Enable for low trust files: If you choose this option, runtime scanning will be enabled for all files for which macros are enabled, except for the following files: Files opened while macro security settings are set to “Enable all macros” Files opened from a trusted location Files that are Trusted Documents Files that contain VBA that is digitally signed by a trusted publisher Enable for all files: If you choose this option, then low trust files are not excluded from runtime scanning. The VBA and XLM runtimes report to an antivirus system certain high-risk code behaviors the macro is about to execute. This allows the antivirus system to indicate whether or not the macro behavior is malicious. If the behavior is determined to be malicious, the Office application closes the session and the antivirus system can quarantine the file. If the behavior is non-malicious, the macro execution proceeds. Note: When macro runtime scanning is enabled, the runtime performance of affected VBA projects and XLM sheets may be reduced. If you disable this policy setting, no runtime scanning of enabled macros will be performed. If you don’t configure this policy setting, “Enable for low trust files” will be the default setting. Note: This policy setting only applies to subscription versions of Office, such as Microsoft 365 Apps for enterprise.

AMSI improves security for all

AMSI provides deep and dynamic visibility into the runtime behaviors of macros and other scripts to expose threats that hide malicious intent behind obfuscation, junk control flow statements, and many other tricks. Microsoft Defender Antivirus, the built-in antivirus solution on Windows 10, has been leveraging AMSI to uncover a wide range of threats, from common malware to sophisticated attacks. The recent AMSI instrumentation in XLM directly tackles the rise of malware campaigns that abuse this feature. Because AMSI is an open interface, other antivirus solutions can leverage the same visibility to improve protections against threats. Security vendors can learn how to leverage AMSI in their antivirus products here.

At Microsoft, we take full advantage of signals from AMSI. The data generated by AMSI is not only useful for immediate client antimalware detections, but also provides rich signals for Microsoft Defender for Endpoint. In our blog post about AMSI for VBA, we described how these signals are ingested by multiple layers of cloud-based machine learning classifiers and are combined with all other signals. The result is an enhanced protection layer that learns to recognize and block new and unknown threats in real-time.

Figure 9. Example of detection from Microsoft Defender Antivirus based on data inspected by AMSI

Figure 10: Notification from Microsoft Excel after AMSI reported malware detection

Figure 11: Example of Microsoft Defender for Endpoint alert for detection of XLM malware

The visibility provided by AMSI leads to significant improvements in generic and resilient signatures that can stop waves of obfuscated and mutated variants of threats. AMSI-driven protection adds to an extensive multi-layer protection stack in Microsoft Defender for Endpoint, which also includes attack surface reduction, network protection, behavior monitoring and other technologies that protect against macro malware and other similar script-based threats.

The AMSI-enriched visibility provided by Microsoft Defender for Endpoint is further amplified across Microsoft 365 Defender, such that XLM macro threats are detected and blocked on various entry vectors. The orchestration of signal-sharing and coordinated defense in Microsoft 365 ensures that, for example, Microsoft Defender for Office 365 blocks macro malware distributed via email, which is the most common delivery methods for these threats.

Learn how you can stop attacks through automated, cross-domain security and built-in AI with Microsoft Defender 365.

 

Giulia Biagini, Office 365 Threat Research Team

Auston Wallace, Microsoft 365 Security Team

Andrea Lelli, Microsoft 365 Defender Threat Intelligence Team

The post XLM + AMSI: New runtime defense against Excel 4.0 macro malware appeared first on Microsoft Security.

Recently, we’ve seen reports of malicious files that misuse the legitimate Office object linking and embedding (OLE) capability to trick users into enabling and downloading malicious content. Previously, we’ve seen macros used in a similar matter, and this use of OLE might indicate a shift in behavior as administrators and enterprises are mitigating against this infection vector with better security and new options in Office.

In these new cases, we’re seeing OLE-embedded objects and content surrounded by well-formatted text and images to encourage users to enable the object or content, and thus run the malicious code. So far, we’ve seen these files use malicious Visual Basic (VB) and JavaScript (JS) scripts embedded in a document.

The script or object is surrounded by text that encourages the user to click or interact with the script (which is usually represented with a script-like icon). When the user interacts with the object, a warning prompts the user whether to proceed or not. If the user chooses to proceed (by clicking Open), the malicious script runs and any form of infection can occur.

Figure 1: Warning message prompts the users to check whether they should open the script or not.

It’s important to note that user interaction and consent is still required to execute the malicious payload. If the user doesn’t enable the object or click on the object – then the code will not run and an infection will not occur.

Education is therefore an important part of mitigation – as with spam emails, suspicious websites, and unverified apps. Don’t click the link, enable the content, or run the program unless you absolutely trust it and can verify its source.

In late May 2016, we came across the following Word document (Figure 2) that used VB script and language similar to that used in CAPTCHA and other human-verification tools.

 

Figure 2: Invitation to unlock contents

 

It’s relatively easy for the malware author to replace the contents of the file (the OLE or embedded object that the user is invited to double-click or activate). We can see this in Figure 3, which indicates the control or script is a JS script.

Figure 3: Possible JavaScript variant

 

The icon used to indicate the object or content can be just about anything. It can be a completely different icon that has nothing to do with the scripting language being used – as the authors can use any pictures and any type

Figure 4: Embedded object variant

 

It’s helpful to be aware of what this kind of threat looks like, what it can look like, and to educate users to not enable, double-click, or activate embedded content in any file without first verifying its source.

Technical details – downloading and decrypting a binary

On the sample we investigated, the contents of the social engineering document is a malicious VB script, which we detect as TrojanDownloader:VBS/Vibrio and TrojanDownloader:VBS/Donvibs. This sample also distinguishes itself from the typical download-and-execute routine common to this type of infection vector – it has a “decryption function”.

This malicious VB script will download an encrypted binary, bypassing any network-based protection designed to recognize malicious formats and block them, decrypt the binary, and then run it. Figure 5 illustrates the encrypted binary we saw in this sample.

Figure 5: The encrypted binary

 

The embedded object or script downloads the encrypted file to %appdata% with a random file name, and proceeds to decrypt it using the script’s decryption function (Figure 6).

Figure 6: Decryption process

Lastly, it executes the now-decrypted binary, which in this example was Ransom:Win32/Cerber.

Figure 7: Decrypted Win32 executable

Prevalence

Our data shows these threats (TrojanDownloader:VBS/Vibrio and TrojanDownloader:VBS/Donvibs) are not particularly prevalent, with the greatest concentration in the United States.

We’ve also seen a steady decline since we first discovered it in late May 2016.

Figure 8: Worldwide prevalence

Figure 9: Daily prevalence

 

Prevention and recovery recommendations

Administrators can prevent activation of OLE packages by modifying the registry key HKCUSoftwareMicrosoftOffice<Office Version><Office application>SecurityPackagerPrompt.

The Office version values should be:

• 16.0 (Office 2016)
• 15.0 (Office 2013)
• 14.0 (Office 2010)
• 12.0 (Office 2007)

 

Setting the value to 2 will cause the  to disable packages, and they won’t be activated if a user tries to interact with or double-click them.

The value options for the key are:

• 0 – No prompt from Office when user clicks, object executes
• 1 – Prompt from Office when user clicks, object executes
• 2 – No prompt, Object does not execute

You can find details about this registry key the Microsoft Support article, https://support.microsoft.com/en-us/kb/926530

 

See our other blogs and our ransomware help page for further guidance on preventing and recovering from these types of attacks:

• Link (.lnk) to Ransom
• The 5Ws and 1H of Ransomware
• Malicious macro using a sneaky new trick
• New feature in Office 2016 can block macros and help prevent infection
• No mas, Samas: What’s in this ransomware’s modus operandi?
• The three heads of the Cerberus-like Cerber ransomware
• Locky malware, lucky to avoid it

 

 

Alden Pornasdoro

MMPC

 

We are alerting Windows users of a new type of ransomware that exhibits worm-like behavior. This ransom leverages removable and network drives to propagate itself and affect more users. We detect this ransomware as Ransom:Win32/ZCryptor.A.

 

Infection vector

Ransom:Win32/ZCryptor.A  is distributed through the spam email infection vector. It also gets installed in your machine through other macro malware*, or fake installers (Flash Player setup).

Once ZCryptor is executed, it will make sure it runs at start-up:

HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun

zcrypt = {path of the executed malware}

 

It also drops autorun.inf in removable drives, a zycrypt.lnk in the start-up folder:

%User Startup%zcrypt.lnk

..along with a copy of itself as {Drive}:system.exe and %appdata%zcrypt.exe, and changes the file attributes to hide itself from the user in file explorer.

For example: c:usersadministratorappdataroamingzcrypt.exe

Payload

This ransomware will display the following ransom note to users in a dropped HTML file How to decrypt files.html:

 

It will also target, encrypt files with the following extension, and change the file extension to .zcrypt once it is done (for example,<originalfilename.zcrypt>):

.accdb	.dwg	.odb	.raf
.apk	.dxg	.odp	.raw
.arw	.emlx	.ods	.rtf
.aspx	.eps	.odt	.rw2
.avi	.erf	.orf	.rwl
.bak	.gz	.p12	.sav
.bay	.html	.p7b	.sql
.bmp	.indd	.p7c	.srf
.cdr	.jar	.pdb	.srw
.cer	.java	.pdd	.swf
.cgi	.jpeg	.pdf	.tar
.class	.jpg	.pef	.tar
.cpp	.jsp	.pem	.txt
.cr2	.kdc	.pfx	.vcf
.crt	.log	.php	.wb2
.crw	.mdb	.png	.wmv
.dbf	.mdf	.ppt	.wpd
.dcr	.mef	.pptx	.xls
.der	.mp4	.psd	.xlsx
.dng	.mpeg	.pst	.xml
.doc	.msg	.ptx	.zip
.docx	.nrw	.r3d	.3fr

 

Infected machines are noticed to have zcrypt1.0 mutex. The mutex denotes that an instance of this ransomware is already running in the infected machine.

We have also seen a connection to the following URL. However, the domain is already down when we were testing:

http://<obfuscated>/rsa/rsa.php?computerid={Computer_ID} where the {Computer_ID} is entry found inside a dropped file %AppData%cid.ztxt

For example, c:usersadministratorappdataroamingcid.ztxt

Prevention

To help stay protected:

• Keep your Windows Operating System and antivirus up-to-date.  Upgrade to Windows 10.
• Regularly back-up your files in an external hard-drive
• Enable file history or system protection. In your Windows 10 or Windows 8.1 devices, you must have your file history enabled and you have to setup a drive for file history
• Use OneDrive for Business
• Beware of phishing emails, spams, and clicking malicious attachment
• Use Microsoft Edge to get SmartScreen protection. It will prevent you from browsing sites that are known to be hosting exploits, and protect you from socially-engineered attacks such as phishing and malware downloads.
• Disable the loading of macros in your Office programs
• Disable your Remote Desktop feature whenever possible
• Use two factor authentication
• Use a safe internet connection
• Avoid browsing web sites that are known for being malware breeding grounds (illegal download sites, porn sites, etc.)

Detection

• Install, use, and regularly update an antivirus solution like Windows Defender to detect ransomware.
• Enable Microsoft Active Protection Service (MAPS) to get the latest cloud-based ransomware detection and blocking.

Recovery

In Office 365’s How to deal with ransomware blog, there are several options on how one can remediate or recover from a ransomware attack. Here are some of the few that are applicable for a home user or those in the information industry like you:

1. Make sure you have backed-up your files.
2. Recover the files in your device. If you have previously turned File History on in Windows 10 and Windows 8.1 devices or System Protection in Windows 7 and Windows Vista devices, you can (in some cases) recover your local files and folders.

To restore your files or folders in Windows 10 and Windows 8.1:

• Swipe in from the right edge of the screen, tap Search (or if you’re using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search). Enter “restore your files” in the search box, and then tap or click Restore your files with File History.
• Enter the name of file you’re looking for in the search box, or use the left and right arrows to browse through different versions of your folders and files.
• Select what you want to restore to its original location, and then tap or click the Restore button. If you want to restore your files onto a different location than the original, press and hold, or right-click the Restore button, tap or click Restore To, and then choose a new location.

Source: Restore files or folders using File History

To restore your files in Windows 7 and Windows Vista

• Right-click the file or folder, and then click Restore previous versions. You’ll see a list of available previous versions of the file or folder. The list will include files saved on a backup (if you’re using Windows Backup to back up your files) as well as restore points. Note: To restore a previous version of a file or folder that’s included in a library, right-click the file or folder in the location where it’s saved, rather than in the library. For example, to restore a previous version of a picture that’s included in the Pictures library but is stored in the My Pictures folder, right-click the My Pictures folder, and then click Restore previous versions. For more information about libraries, see Include folders in a library.
• Before restoring a previous version of a file or folder, select the previous version, and then click Open to view it to make sure it’s the version you want. Note: You can’t open or copy previous versions of files that were created by Windows Backup, but you can restore them.
• To restore a previous version, select the previous version, and then click Restore.

Warning: The file or folder will replace the current version on your computer, and the replacement cannot be undone. Note: If the Restore button isn’t available, you can’t restore a previous version of the file or folder to its original location. However, you might be able to open it or save it to a different location.

Source: Previous versions of files: frequently asked questions

Important: Some ransomware will also encrypt or delete the backup versions and will not allow you to do the actions described before. If this is the case, you need to rely on backups in external drives (not affected by the ransomware) or OneDrive (Next step).

Warning: If the folder is synced to OneDrive and you are not using the latest version of Windows, there might be some limitations using File History.

1. Recover your files in your OneDrive for Consumer
   • Find lost or missing files in OneDrive
   • Delete or restore files and folders
2. Recover your files in your OneDrive for Business

If you use OneDrive for Business, it will allow you to recover any files you have stored in it. You can use either of the following options:

Restore your files using the Portal

Users can restore previous version of the file through the user interface. To do this you can:

1. Go to OneDrive for Business in the office.com portal

2. Right click the file you want to recover, and select Version History.

3. Click the dropdown list of the version you want to recover and select restore

 

If you want to learn more about this feature, take a look at the Restore a previous version of a document in OneDrive for Business support article.

Create a Site Collection Restore service request

If a large number of files were impacted, using the user interface in the portal will not be a viable option. In this case, create a support request for a ‘Site Collection Restore’. This request can restore up to 14 days in the past. To learn how to do this please take a look at the Restore Option in SharePoint Online blog post.

 

*Related macro malware information:

• Malicious macro using a sneaky new trick
• New feature in Office 2016 can block macros and help prevent infection
• Threat intel on macro malware
• Macro malware

 

Edgardo Diaz and Marianne Mallen

Microsoft Malware Protection Center (MMPC)

The macro malware-laden documents that target email users through email spam are intentionally crafted to pique any person's curiosity.  With subjects that include sales invoices, federal tax payments, courier notifications, resumes, and donation confirmations, users can be easily tricked to read the email and open the attachment without thinking twice.

The user opens the document, enables the macro, thinking that the document needs it to function properly – unknowingly enabling the macro malware to run.

Just when you think macro malware is a thing of the past, over the past few months, we have seen an increasing macro downloader trend that affects nearly 501,240 unique machines worldwide.

 Figure 1: Increasing trend of macro downloaders from April 2014 to 2015

We have seen majority of the macro-malware attacks in the United States and United Kingdom.

Figure 2: Macro downloaders’ prevalence in affected countries

 

Figure 3: Macro malware distribution heat map

Macro malware infection chain

As stated in the previous macro blog, macro downloaders serve as the gateway for other nasty malware to get in. The following diagram shows how a typical macro downloader gets into the system and deliver its payload.

Figure 4: Macro downloader infection chain

The macro malware gets into your PC as a spam email attachment. The spam email recipient then falls for a social engineering technique, opens the attachment, thereby enabling the macro inside the document.

We have identified some of these macro downloader threats, but not limited to:

• Adnel
• Bartallex
• Donoff
• Jeraps
• Ledod

When a malicious macro code runs, it either downloads its final payload, or it downloads another payload courier in the form of a binary downloader.

We have observed the following final payload, but is not limited to:

• TrojanSpy:MSIL/Golroted

We have also observed the following binary downloaders to be related to these macros, but not limited to:

• TrojanDownloader:Win32/Drixed
• TrojanDownloader:Win32/Chanitor

After the macro malware is downloaded, the job is pretty much done. The torch is passed to either the final payload or the binary downloader.

We have observed the following threats being downloaded by the binary downloaders, but not limited to:

• Backdoor:Win32/Drixed
• Backdoor:Win32/Vawtrak

 

Prevention: How do you close that door?

If you know that social engineering tricks through spam emails open the door to macro malware attacks, what can you do to help protect your enterprise software security infrastructure in closing that door?

Be careful on enabling macros

Macro threats, as payload couriers, seem to gain popularity as an effective infection vector. But unlike exploit kits, these macro threats require user consent to run. To avoid running into trouble because of these macro threats, see Before you enable those macros, for details on prevention.

You can also read more about the macro configuration options to understand the scenarios when you can enable or disable them. See Microsoft Project – how to control Macro Settings using registry keys for details.

Aside from that, be aware of the dangers in opening suspicious emails. That includes not opening email attachments or links from untrusted sources.

If you are an enterprise software security administrator, what can you do?

Most, if not all of the macro malware received are in .doc file format (D0 CF) which are seen in Microsoft Office 2007 and older versions.

If you are in charge of looking after your enterprise software security infrastructure, you can:

• Update your Microsoft security software. Microsoft detects this threat and encourages everyone to always run on the latest software version for protection.
• Ensure that your Trust Center settings are configured not to load older Office versions:

1. Go to Word Options, and select Trust Center. Click Trust Center Settings.

   

                                                               

2. In the Trust Center dialog box, select File Block Settings. Then, select the Word versions that you need to block. 

Doing so blocks older Office versions from opening.

• Follow the appropriate Exchange Online Protection instructions to suite your business needs.
• Learn some insights on how Office 365 can help you block spams using machine learning. See First look at Advanced Threat Protection: new tools to stop unknown malware & phishing attacks for details.
• Submit spam and non-spam messages to Microsoft for analysis.
• Enable the Microsoft Active Protection Service (MAPS). Customers using MAPS can take advantage of Microsoft's cloud protection and are protected with the latest threat variants. MAPS is enabled by default for Microsoft Security Essentials and Windows Defender for Windows 8.1.

You can check if MAPS feature is enabled in your Microsoft security product by selecting the Settings tab and then MAPS.

MMPC

The macro malware-laden documents that target email users through email spam are intentionally crafted to pique any person's curiosity.  With subjects that include sales invoices, federal tax payments, courier notifications, resumes, and donation confirmations, users can be easily tricked to read the email and open the attachment without thinking twice.

The user opens the document, enables the macro, thinking that the document needs it to function properly – unknowingly enabling the macro malware to run.

Just when you think macro malware is a thing of the past, over the past few months, we have seen an increasing macro downloader trend that affects nearly 501,240 unique machines worldwide.

 Figure 1: Increasing trend of macro downloaders from April 2014 to 2015

We have seen majority of the macro-malware attacks in the United States and United Kingdom.

Figure 2: Macro downloaders’ prevalence in affected countries

 

Figure 3: Macro malware distribution heat map

Macro malware infection chain

As stated in the previous macro blog, macro downloaders serve as the gateway for other nasty malware to get in. The following diagram shows how a typical macro downloader gets into the system and deliver its payload.

Figure 4: Macro downloader infection chain

The macro malware gets into your PC as a spam email attachment. The spam email recipient then falls for a social engineering technique, opens the attachment, thereby enabling the macro inside the document.

We have identified some of these macro downloader threats, but not limited to:

• Adnel
• Bartallex
• Donoff
• Jeraps
• Ledod

When a malicious macro code runs, it either downloads its final payload, or it downloads another payload courier in the form of a binary downloader.

We have observed the following final payload, but is not limited to:

• TrojanSpy:MSIL/Golroted

We have also observed the following binary downloaders to be related to these macros, but not limited to:

• TrojanDownloader:Win32/Drixed
• TrojanDownloader:Win32/Chanitor

After the macro malware is downloaded, the job is pretty much done. The torch is passed to either the final payload or the binary downloader.

We have observed the following threats being downloaded by the binary downloaders, but not limited to:

• Backdoor:Win32/Drixed
• Backdoor:Win32/Vawtrak

 

Prevention: How do you close that door?

If you know that social engineering tricks through spam emails open the door to macro malware attacks, what can you do to help protect your enterprise software security infrastructure in closing that door?

Be careful on enabling macros

Macro threats, as payload couriers, seem to gain popularity as an effective infection vector. But unlike exploit kits, these macro threats require user consent to run. To avoid running into trouble because of these macro threats, see Before you enable those macros, for details on prevention.

You can also read more about the macro configuration options to understand the scenarios when you can enable or disable them. See Microsoft Project – how to control Macro Settings using registry keys for details.

Aside from that, be aware of the dangers in opening suspicious emails. That includes not opening email attachments or links from untrusted sources.

If you are an enterprise software security administrator, what can you do?

Most, if not all of the macro malware received are in .doc file format (D0 CF) which are seen in Microsoft Office 2007 and older versions.

If you are in charge of looking after your enterprise software security infrastructure, you can:

• Update your Microsoft security software. Microsoft detects this threat and encourages everyone to always run on the latest software version for protection.
• Ensure that your Trust Center settings are configured not to load older Office versions:

1. Go to Word Options, and select Trust Center. Click Trust Center Settings.

   

                                                               

2. In the Trust Center dialog box, select File Block Settings. Then, select the Word versions that you need to block. 

Doing so blocks older Office versions from opening.

• Follow the appropriate Exchange Online Protection instructions to suite your business needs.
• Learn some insights on how Office 365 can help you block spams using machine learning. See First look at Advanced Threat Protection: new tools to stop unknown malware & phishing attacks for details.
• Submit spam and non-spam messages to Microsoft for analysis.
• Enable the Microsoft Active Protection Service (MAPS). Customers using MAPS can take advantage of Microsoft's cloud protection and are protected with the latest threat variants. MAPS is enabled by default for Microsoft Security Essentials and Windows Defender for Windows 8.1.

You can check if MAPS feature is enabled in your Microsoft security product by selecting the Settings tab and then MAPS.

MMPC