Microsoft has released a security advisory about a remote code execution vulnerabilities affecting all currently supported versions of Windows and Windows Server operating systems.



According to advisory [1], a remote attacker can exploit these vulnerabilities, affecting the Adobe Type Manager Library, to take control of an affected system.

Some details about vulnerabilities

https://twitter.com/msftsecresponse/status/1242135309116043270?ref_src=twsrc%5Etfw

Adobe Type Manager, which is provided by atmfd.dll, is a kernel module that is provided by Windows and provides support for OpenType fonts.
Using a specially crafted document opened or view it in the Windows preview pane, an unauthenticated remote attacker may be able to execute arbitrary code with kernel privileges on a vulnerable system.

On Windows 10, exploting this vulnerabilities allows code execution with limited privileges, in an AppContainer sandbox.

Fixes or Mitigations

https://twitter.com/rosyna/status/1242156545346916352?ref_src=twsrc%5Etfw

Currently, there is no patch. According to Microsoft's advisory [1]:

Microsoft is aware of this vulnerability and working on a fix. Updates that address security vulnerabilities in Microsoft software are typically released on Update Tuesday, the second Tuesday of each month. This predictable schedule allows for partner quality assurance and IT planning, which helps maintain the Windows ecosystem as a reliable, secure choice for our customers. The operating system versions that are affected by this vulnerability are listed below.

So, Microsoft proposed some mitigations:

Rename ATMFD.DLL

This mitigation appears to be to the most effective workaround for this vulnerability, as it blocks the vulnerable code from being used by Windows.
However, because supported Windows 10 versions do not use ATMFD.DLL, this mitigation is not applicable on this systems.

For 32-bit systems:

Enter the following commands at an administrative command prompt and restart the system:

cd "%windir%\system32"
takeown.exe /f atmfd.dll
icacls.exe atmfd.dll /save atmfd.dll.acl
icacls.exe atmfd.dll /grant Administrators:(F) 
rename atmfd.dll x-atmfd.dll

For 64-bit systems:

Enter the following commands at an administrative command prompt and restart the system:

	cd "%windir%\system32"
	takeown.exe /f atmfd.dll
	icacls.exe atmfd.dll /save atmfd.dll.acl
	icacls.exe atmfd.dll /grant Administrators:(F) 
	rename atmfd.dll x-atmfd.dll
	cd "%windir%\syswow64"
	takeown.exe /f atmfd.dll
	icacls.exe atmfd.dll /save atmfd.dll.acl
	icacls.exe atmfd.dll /grant Administrators:(F) 
	rename atmfd.dll x-atmfd.dll

Disable the preview pane and details pane in Windows Explorer

Disabling the Preview and Details panes in Windows Explorer prevents the automatic display of OTF fonts in Windows Explorer. While this prevents malicious files from being viewed in Windows Explorer, it does not prevent a local, authenticated user from running a specially crafted program to exploit this vulnerability.

To disable these panes in Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows 8.1, perform the following steps:

  1. Open Windows Explorer, click Organize, and then click Layout.
  2. Clear both the Details pane and Preview pane menu options.
  3. Click Organize, and then click Folder and search options.
  4. Click the View tab.
  5. Under Advanced settings, check the Always show icons, never thumbnails box.
  6. Close all open instances of Windows Explorer for the change to take effect.

For Windows Server 2016, Windows 10, and Windows Server 2019, perform the following steps:

  1. Open Windows Explorer, click the View tab.
  2. Clear both the Details pane and Preview pane menu options.
  3. Click Options, and then click Change folder and search options.
  4. Click the View tab.
  5. Under Advanced settings, check the Always show icons, never thumbnails box.
  6. Close all open instances of Windows Explorer for the change to take effect.

Disable the WebClient service

Disabling the WebClient service helps protect affected systems from attempts to exploit this vulnerability by blocking the most likely remote attack vector through the Web Distributed Authoring and Versioning (WebDAV) client service. After applying this workaround it is still possible for remote attackers who successfully exploit this vulnerability to cause the system to run programs located on the targeted user's computer or the Local Area Network (LAN), but users will be prompted for confirmation before opening arbitrary programs from the Internet.

To disable the WebClient Service, perform the following steps:

  1. Click Start, click Run (or press the Windows Key and R on the keyboard), type Services.msc and then click OK.
  2. Right-click WebClient service and select Properties.
  3. Change the Startup type to Disabled. If the service is running, click Stop.
  4. Click OK and exit the management application.

References

  1. ADV200006 | Type 1 Font Parsing Remote Code Execution Vulnerability