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CVE-2020-0938HIGH · 7.8Plan to patch

Microsoft Windows Adobe Font Manager Library Remote Code Execution Vulnerability

CVE-2020-0938 is a security vulnerability in Microsoft Windows, added to CISA KEV on November 3, 2021. Patch priority: Plan to patch.

Added to CISA KEV November 3, 2021 · Microsoft Windows

What it is

Microsoft Windows Adobe Font Manager Library contains an unspecified vulnerability when handling specially crafted multi-master fonts (Adobe Type 1 PostScript format) that allows for remote code execution for all systems except Windows 10. For systems running Windows 10, an attacker who successfully exploited the vulnerability could execute code in an AppContainer sandbox context with limited privileges and capabilities.

VulnCheck tracked exploitation 568 days before CISA's KEV listing. VulnCheck's broader catalog of in-the-wild exploitation evidence picked this up before it landed on CISA's formal list. Per-CVE fact about this entry; not a population claim about lead time in general.

Who's affected

Affects anyone running Windows workstations or servers. In a small CPA, legal, or dental practice, Windows is typically the platform your accounting, document management, or practice management software runs on — exploitation gives an attacker access to whatever client files and credentials live on those machines.

What to do

Apply updates per vendor instructions.

If you don't have someone in-house to verify the patch deployed across every endpoint — or you're not sure whether you're affected — that's exactly the kind of triage we do. Book a free 20-minute triage call.

Insurance readiness

Your insurer will ask if this is patched.

Unpatched entries on CISA's Known Exploited Vulnerabilities list are exactly what cyber-insurance carrier questionnaires probe for, and knowing which controls they check is how you keep a renewal from stalling.

Get the free carrier questionnaire →

Severity

CVSS base score: 7.8 — HIGH

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Weakness classification: CWE-787

CVSS, severity, and CWE data from the National Vulnerability Database (NVD). This product uses data from the NVD API but is not endorsed or certified by the NVD.

Microsoft fix

  • KB4550922 (Security Update)
  • KB4549949 (Security Update)
  • KB4549951 (Security Update)
  • KB4550927 (Security Update)
  • KB4550930 (Security Update)
  • KB4550929 (Security Update)
  • KB4550964 (Monthly Rollup)
  • KB4550965 (Security Only)
  • KB4550961 (Monthly Rollup)
  • KB4550970 (Security Only)
  • KB4550951 (Monthly Rollup)
  • KB4550957 (Security Only)
  • KB4550917 (Monthly Rollup)
  • KB4550971 (Security Only)

Microsoft Exploitability Index (assessed at update release): Exploitation Less Likely

This CVE is on CISA's Known Exploited Vulnerabilities catalog. Microsoft's index reflects their release-time forecast, not current observed activity, and is not automatically revised upward when exploitation appears later.

Sourced from Microsoft Security Update Guide (CVRF document 2020-Apr).

Vendor workaround

Vendor-published workaround

There are several different workarounds in this section. Not all may apply to all networks.

Workaround Applicability
Disable the Preview Pane and Details Pane in Windows Explorer Works on all systems but won't mitigate the issue if you open a document with the vulnerable font class
Disable the WebClient service Works on all systems but won't mitigate the issue if you open a document with the vulnerable font class
DisableATMFD registry key using a managed deployment script Only works on older (before Windows 10) but completely mitigates the issue though can introduce usability issues in rare cases
DisableATMFD registry key manually Only works on older (before Windows 10) but completely mitigates the issue though can introduce usability issues in rare cases
Rename ATMFD.DLL Only works on older (before Windows 10) but completely mitigates the issue though can introduce usability issues in rare cases

Note: We do not recommend that IT administrators running Windows 10 implement the workarounds described below. ATMFD.DLL is not present in Windows 10 installations starting with Windows 10, version 1709. Newer versions do not have this DLL. See the Mitigation section for more information.

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.

To disable these panes in all supported client and server versions of Windows 10, 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.

Impact of workaround.

Windows Explorer will not automatically display OTF fonts.

How to undo the workaround.

To re-enable the Preview and Details panes in Windows Explorer for Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows 8.1:

  1. Open Windows Explorer, click Organize, and then click Layout.
  2. Select 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, clear the Always show icons, never thumbnails box.
  6. Close all open instances of Windows Explorer for the change to take effect.

To re-enable the Preview and Details panes in Windows Explorer for all supported client and server versions of Windows 10, perform the following steps:

  1. Open Windows Explorer, click the View tab.
  2. Select 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, clear 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.

Impact of workaround.

When the WebClient service is disabled, Web Distributed Authoring and Versioning (WebDAV) requests are not transmitted. In addition, any services that explicitly depend on the WebClient service will not start, and an error message will be logged in the System log. For example, WebDAV shares will be inaccessible from the client computer.

How to undo the workaround.

To re-enable 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 Automatic. If the service is not running, click Start.
  4. Click OK and exit the management application.

DisableATMFD registry key using a managed deployment script

Please Note: This workaround works for Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows 8.1. ATMFD.DLL is not present in Windows 10 installations starting with Windows 10, version 1709.

Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

  1. Create a text file named ATMFD-disable.reg that contains the following text:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows]
"DisableATMFD"=dword:00000001
  1. Run regedit.exe.
  2. In Registry Editor, click the File menu and then click Import.
  3. Navigate to and select the** ATMFD-disable.reg** file that you created in the first step. (Note If your file is not listed where you expect it to be, ensure that it has not been automatically given a .txt file extension, or change the dialog’s file extension parameters to All Files).
  4. Click Open and then click OK to close Registry Editor.
  5. Restart the system.

Impact of workaround

Applications that rely on embedded font technology will not display properly. Renaming ATMFD.DLL could cause certain applications to stop working properly if they use OpenType fonts. Microsoft Windows does not release any OpenType fonts natively. However, third-party applications could install them and they could be affected by this change.

How to undo the workaround.

  1. Create a text file named ATMFD-enable.reg that contains the following text:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows]
"DisableATMFD"=dword:00000000
  1. Run regedit.exe.
  2. In Registry Editor, click the File menu and then click Import.
  3. Navigate to and select the ATMFD-enable.reg file that you created in the first step. (Note If your file is not listed where you expect it to be, ensure that it has not been automatically given a .txt file extension, or change the dialog’s file extension parameters to All Files).
  4. Click Open and then click OK to close Registry Editor.
  5. Restart the system.

DisableATMFD registry key manually

Please Note: This workaround works for Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows 8.1. ATMFD.DLL is not present in Windows 10 installations starting with Windows 10, version 1709. Newer versions do not have this DLL. See the Mitigation section for more information.

Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

  1. Run regedit.exe as Administrator.
  2. In Registry Editor, navigate to the following sub key (or create it) and set its DWORD value to 1: HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows\DisableATMFD, DWORD = 1
  3. Close Registry Editor and restart the system.

Impact of workaround

Applications that rely on embedded font technology will not display properly. Renaming ATMFD.DLL could cause certain applications to stop working properly if they use OpenType fonts. Microsoft Windows does not release any OpenType fonts natively. However, third-party applications could install them and they could be affected by this change.

How to undo the workaround.

  1. Run regedit.exe as Administrator.
  2. In Registry Editor, navigate to the following sub key and set its DWORD value to 0: HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows\DisableATMFD, DWORD = 0
  3. Close Registry Editor and restart the system.

Rename ATMFD.DLL

Please Note: This workaround works for Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows 8.1. ATMFD.DLL is not present in Windows 10 installations starting with Windows 10, version 1709. Newer versions do not have this DLL. See the Mitigation section for more information.

For 32-bit systems:

  1. Enter the following commands at an administrative command prompt:
 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
  1. Restart the system.

For 64-bit systems:

  1. Enter the following commands at an administrative command prompt:
	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
  1. Restart the system.

Impact of workaround

Applications that rely on embedded font technology will not display properly. Renaming ATMFD.DLL could cause certain applications to stop working properly if they use OpenType fonts. Microsoft Windows does not release any OpenType fonts natively. However, third-party applications could install them and they could be affected by this change.

How to undo the workaround

For 32-bit systems:

  1. Enter the following commands at an administrative command prompt:
	cd "%windir%\system32"
	rename x-atmfd.dll atmfd.dll
	icacls.exe atmfd.dll /setowner "NT SERVICE\TrustedInstaller"
	icacls.exe . /restore atmfd.dll.acl
  1. Restart the system.

For 64-bit systems:

  1. Enter the following commands at an administrative command prompt:
	cd "%windir%\system32"
	rename x-atmfd.dll atmfd.dll
	icacls.exe atmfd.dll /setowner "NT SERVICE\TrustedInstaller"
	icacls.exe . /restore atmfd.dll.acl
	cd "%windir%\syswow64"
	rename x-atmfd.dll atmfd.dll
	icacls.exe atmfd.dll /setowner "NT SERVICE\TrustedInstaller"
	icacls.exe . /restore atmfd.dll.acl
  1. Restart the system.

Vendor-published mitigation

For systems running supported versions of Windows 10 a successful attack could only result in code execution within an AppContainer sandbox context with limited privileges and capabilities.

Version Fonts Process With
Windows 10 fontdrvhost.exe in user mode appcontainer. Installed fonts are still processed in kernel mode
Windows 10 Version 1607/Server 2016 fontdrvhost.exe in user mode appcontainer. Installed fonts are still processed in kernel mode
Windows 10 1703 All fonts are processed in fontdrvhost.exe in user mode appcontainer.
Windows 10 1709 All fonts are processed in fontdrvhost.exe in user mode appcontainer.
Windows 10 1803/Windows Server, version 1803 All fonts are processed in fontdrvhost.exe in user mode appcontainer.
Windows 10 1809/Server 2019 All fonts are processed in fontdrvhost.exe in user mode appcontainer.
Windows 10 1903/Windows Server, version 1903 All fonts are processed in fontdrvhost.exe in user mode appcontainer.
Windows 10 1909/Windows Server, version 1909 All fonts are processed in fontdrvhost.exe in user mode appcontainer.

For more information, see Mitigating font exploits with AppContainer.

A workaround reduces exposure while you patch — it is not a substitute for the update. Install the fix above as soon as you can.

Shown as published by Microsoft (Security Update Guide, CVRF document 2020-Apr); formatting sanitized, content unaltered.

CISA due date

Federal deadline: May 3, 2022. Federal agencies must complete the required action by this date. For private SMBs the deadline is advisory — but treat it as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).

EPSS

EPSS score: 69.2% — higher than 99% of all scored CVEs.

EPSS estimates the probability of exploitation activity in the next 30 days. Every entry on this site is already confirmed exploited, so read it as relative urgency among the things you still have open, not as permission to wait.

Score dated 2026-08-12, from the FIRST.org Exploit Prediction Scoring System.

Other exploited Microsoft Windows entries

More CISA KEV entries for Microsoft Windows. Same product line, same actively-exploited status.

  • CVE-2008-4250: Microsoft Windows Buffer Overflow Vulnerability
  • CVE-2026-32202: Microsoft Windows Protection Mechanism Failure Vulnerability
  • CVE-2025-60710: Microsoft Windows Link Following Vulnerability
  • CVE-2023-36424: Microsoft Windows Out-of-Bounds Read Vulnerability
  • CVE-2008-0015: Microsoft Windows Video ActiveX Control Remote Code Execution Vulnerability
  • CVE-2026-21519: Microsoft Windows Type Confusion Vulnerability
  • CVE-2026-21513: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability
  • CVE-2026-21533: Microsoft Windows Improper Privilege Management Vulnerability

Browse more

  • All Microsoft KEV entries
  • Windows
  • All SMB-relevant KEV entries

Source

This entry comes from CISA's Known Exploited Vulnerabilities catalog, public US-Government data we pull daily. The plain-language framing and the what-to-do guidance above are ours. View the original entry on cisa.gov.

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