Malicious SettingContent now delivered through PDF

Recently, a proof-of-concept emerged on how the filetype SettingContent can be abused when getting embedded in Microsoft Office Documents. SettingContent is a feature in Windows 10 which acts as a shortcut to different system settings. Legitimate examples of this can be found in %windir%\ImmersiveControlPanel\Settings (e.g. %windir%\ImmersiveControlPanel\Settings\CortanaSettings.settingcontent-ms will launch Microsoft's Cortana when double clicked). In response, Microsoft updated the Packager Activation list so that Office 365 can now block SettingContent within an OLE package.

As expected, malware authors found another way to utilize the same technique of delivering malicious files through the filetype SettingContent. However this time, they have it embedded in PDF files.

We recently came across PDF samples with embedded .SettingContent-ms getting spammed in the wild. Although the email body does contain any deceptive or luring pretext, the cleverly named attachment can mislead curious users to click on it thinking that the attachment is a legitimate invoice pdf.

Email_sample
Figure 1: Email sample containing a malicious PDF attachment

 

Malware Analysis:

Upon execution of the PDF attachment "INV 60542183.pdf", an embedded javascript object will run. Acrobat will prompt the user with a security warning regarding another object "downl.SettingContent-ms" that is about to be opened. Once the user agrees, it will be saved at the %temp% folder and executed. Afterwards, this will be deleted by Acrobat from the system.

Pdf-sc
Figure 2: Security warning triggered when PDF attachment is opened

JsFigure 3: The javascript object uses exportDataObject to launch "downl.SettingContent-ms"

 

The object "downl.SettingContent-ms" is an XML file recognized in the system as filetype SettingContent. It contains a DeepLink element which will execute any code within the <DeepLink/> tag. In this case, the code invokes PowerShell to download a binary silently into the system, then execute as "%temp%\update12.exe".

Seg_email_sample
Figure 4: The embedded object "downl.SettingContent-ms" extracted by SEG

 

The downloaded binary "%temp%\update12.exe" will connect to hxxp://169.239.128.164/sd87f67ds5gs7d5fs7df to fetch an encrypted blob and decrypt it as "%programdata%\Microsoft Help\wsus.exe". This is the final payload known as FlawedAmmyy version 3.

Flawedammy_v3_ida
Figure 5: FlawedAmmy version 3

 

FlawedAmmyy is a remote access trojan that has the following features:

  • View screen
  • Remote control
  • File manager
  • Audio chat
  • RDP sessions

It can also retrieve system information and send them to the C&C.

Param_ida
Figure 6: Screenshot of the parameters being sent to the FlawedAmmyy C&C

 

Conclusion:

The exploitable component of SettingContent is its DeepLink element since any code in it will be executed without any warning to the user. As the misuse of SettingContent has been addressed by Microsoft, malware authors looked for another way to deliver their malicious intent using this filetype. Now, it's via PDF.

 

IOCs:

Filename

Size

(bytes)

Sha256

Codename

Download URL

INV 60542183.pdf

2,345

0A4F3F9ACC61B85183108A31A306115FE34B571240DA70920F0A1425FC32C3DE

PDF Attachment

-

%temp%\update12.exe

172,032

7db2e889b3156f3ebaea1340a129845b4935361e8cdcf92b430d64c96ac26014

Downloader

hxxp://169.239.128.164/tov

-

665032

618A1942370F4F0725FB2A28D85B7ACA828051F50079D51364A9B8AA19108F8

Encrypted blob

hxxp://169.239.128.164/sd87f67ds5gs7d5fs7df

%programdata%\Microsoft Help\wsus.exe

665032

56f1ab4b108cafcbada89f5ca52ed7cdaf51c6da0368a08830ca8e590d793498

FlawedAmmyy RAT

-

 

 

 

 

 

 

 

 




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