CriticalCVE-2020-0938

    Microsoft Windows Adobe Font Manager Library Remote Code Execution Vulnerability (CVE-2020-0938)

    Published In CISA KEV since Sources: Schneider Electric, CVE.org

    What is affected, what to do

    A remote code execution vulnerability exists in Microsoft Windows when the Windows Adobe Type Manager Library improperly handles a specially-crafted multi-master font - Adobe Type 1 PostScript format.For all systems except Windows 10, an attacker who successfully exploited the vulnerability could execute code remotely, aka 'Adobe Font Manager Library Remote Code Execution Vulnerability'. This CVE ID is unique from CVE-2020-1020.

    The vulnerability is being actively exploited; treat it as a priority. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows eq 10 Version 1803 for 32-bit Systems..10 Version 1803 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1803 for x64-based Systems..10 Version 1803 for x64-based Systems
    • Microsoft Windows eq 10 Version 1803 for ARM64-based Systems..10 Version 1803 for ARM64-based Systems
    • Microsoft Windows eq 10 Version 1809 for 32-bit Systems..10 Version 1809 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1809 for x64-based Systems..10 Version 1809 for x64-based Systems
    • Microsoft Windows eq 10 Version 1809 for ARM64-based Systems..10 Version 1809 for ARM64-based Systems
    • Microsoft Windows eq 10 Version 1709 for 32-bit Systems..10 Version 1709 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1709 for x64-based Systems..10 Version 1709 for x64-based Systems
    • Microsoft Windows eq 10 Version 1709 for ARM64-based Systems..10 Version 1709 for ARM64-based Systems
    • Microsoft Windows eq 10 for 32-bit Systems..10 for 32-bit Systems
    • Microsoft Windows eq 10 for x64-based Systems..10 for x64-based Systems
    • Microsoft Windows eq 10 Version 1607 for 32-bit Systems..10 Version 1607 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1607 for x64-based Systems..10 Version 1607 for x64-based Systems
    • Microsoft Windows eq 7 for 32-bit Systems Service Pack 1..7 for 32-bit Systems Service Pack 1
    • Microsoft Windows eq 7 for x64-based Systems Service Pack 1..7 for x64-based Systems Service Pack 1
    • Microsoft Windows eq 8.1 for 32-bit systems..8.1 for 32-bit systems
    • Microsoft Windows eq 8.1 for x64-based systems..8.1 for x64-based systems
    • Microsoft Windows eq RT 8.1..RT 8.1
    • Microsoft Windows Server eq version 1803 (Core Installation)..version 1803 (Core Installation)
    • Microsoft Windows Server eq 2019..2019
    • Microsoft Windows Server eq 2019 (Core installation)..2019 (Core installation)
    • Microsoft Windows Server eq 2016..2016
    • Microsoft Windows Server eq 2016 (Core installation)..2016 (Core installation)
    • Microsoft Windows Server eq 2008 for 32-bit Systems Service Pack 2..2008 for 32-bit Systems Service Pack 2
    • Microsoft Windows Server eq 2008 for 32-bit Systems Service Pack 2 (Core installation)..2008 for 32-bit Systems Service Pack 2 (Core installation)
    • Microsoft Windows Server eq 2008 for Itanium-Based Systems Service Pack 2..2008 for Itanium-Based Systems Service Pack 2
    • Microsoft Windows Server eq 2008 for x64-based Systems Service Pack 2..2008 for x64-based Systems Service Pack 2
    • Microsoft Windows Server eq 2008 for x64-based Systems Service Pack 2 (Core installation)..2008 for x64-based Systems Service Pack 2 (Core installation)
    • Microsoft Windows Server eq 2008 R2 for Itanium-Based Systems Service Pack 1..2008 R2 for Itanium-Based Systems Service Pack 1
    • Microsoft Windows Server eq 2008 R2 for x64-based Systems Service Pack 1..2008 R2 for x64-based Systems Service Pack 1
    • Microsoft Windows Server eq 2008 R2 for x64-based Systems Service Pack 1 (Core installation)..2008 R2 for x64-based Systems Service Pack 1 (Core installation)
    • Microsoft Windows Server eq 2012..2012
    • Microsoft Windows Server eq 2012 (Core installation)..2012 (Core installation)
    • Microsoft Windows Server eq 2012 R2..2012 R2
    • Microsoft Windows Server eq 2012 R2 (Core installation)..2012 R2 (Core installation)

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Schneider Electric, CVE.org

    69.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.35

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    217.96 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: ANSSI / CERT-FR How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    69.0 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.35
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary

    Response and mitigation

    Why act now?

    Prioritisation rationale

    With an EPSS score in the 99.3rd percentile, CVE-2020-0938 sits among the most likely-to-be-exploited vulnerabilities tracked by FIRST, and its presence on the CISA KEV list since November 2021 confirms active exploitation. The CVSS:3.1 vector (AV:L/AC:L/PR:N/UI:R) reflects a low-complexity local attack requiring only a single user interaction — previewing or opening a document containing a crafted Type 1 PostScript font — with no privilege requirement. For all Windows versions prior to Windows 10, exploitation yields full, unsandboxed RCE, making unpatched Windows Server 2012 instances and older Windows 10 builds in KRITIS or NIS2-regulated environments a high-priority remediation target. Organisations still running Windows Server 2012 in production or Windows 10 builds below 1803 should treat this as critical and front-load patch deployment ahead of other pending updates.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Apply the patch: Deploy Microsoft's April 2020 Patch Tuesday update for all affected systems — Windows Server 2012 and Windows 10 versions 1507, 1607, and 1709. Look up the specific KB number for each OS version in the Microsoft Security Response Center advisory for CVE-2020-0938.
      • Prioritise legacy systems: Windows Server 2012 and Windows 10 builds prior to 1803 are fully exposed to unrestricted RCE (no AppContainer sandbox). Patch or isolate these assets before all others.
      • Disable Windows Explorer preview pane: Via Group Policy — User Configuration → Administrative Templates → Windows Components → Windows Explorer → Turn off the Preview Pane — prevents automatic font rendering triggered by file browsing.
      • Stop and disable the WebClient service: Run sc stop WebClient && sc config WebClient start=disabled on all affected hosts. This removes the WebDAV/UNC remote trigger path that allows a crafted font file to be fetched and parsed without user download.
      • Block outbound SMB at the perimeter: Drop TCP 445 to external destinations at the firewall to prevent UNC-path-based font loading from reaching attacker-controlled shares.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place workstations in dedicated VLANs; restrict outbound TCP 445 and TCP 80/443 to non-inventoried destinations — prevents crafted font files from being pulled over network shares.
      • Disable the Adobe Type Manager Font Driver: Apply the Microsoft-documented registry workaround: set HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\DisableATMFD (DWORD) to 1. This fully disables atmfd.dll. Note: may cause rendering issues for Type 1 fonts in legacy applications.
      • AppLocker / WDAC policy: Restrict process execution from %TEMP% and %APPDATA% to block post-exploitation payload staging after successful font parsing.
      • Mail and proxy gateway filtering: Quarantine or block inbound attachments with extensions .otf, .pfb, .pfm, .ps, and .eps at the email gateway and web proxy.
      • IPS signature coverage: Enable IPS signatures for anomalous SMB sessions carrying embedded font resources; configure a Suricata rule alerting on outbound SMB connections from workstations to external IPs within seconds of a document-open event.
      • Least privilege enforcement: Confirm that end users do not hold local administrator rights — limits blast radius to the user context if exploitation succeeds.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 7 (Image Load): Alert on atmfd.dll or atmlib.dll loaded by unexpected parent processes (e.g., explorer.exe spawning a child that loads atmfd.dll). Sigma shape: ImageLoaded|endswith: 'atmfd.dll' AND ParentImage|contains: 'explorer'.
      • Sysmon EID 1 / Windows EID 4688: Process creation — spoolsv.exe or svchost.exe spawning cmd.exe or powershell.exe shortly after a document or font file is opened. KQL snippet: EventID == 1 and ParentImage endswith "spoolsv.exe" and Image endswith "cmd.exe".
      • Network telemetry (Zeek / Suricata): Outbound SMB connections (TCP 445) from workstations to external or unknown internal hosts within a short window of a file-open event. Filter Zeek field smb_files.name for .otf and .pfb extensions.
      • File-system audit (Windows Security EID 4663): Log access to C:\Windows\System32\atmfd.dll or C:\Windows\SysWOW64\atmfd.dll by non-SYSTEM processes. Any non-system process touching this DLL outside of a patching window is suspicious.
      • EDR process tree: Alert on the chain explorer.exe → dllhost.exe → [unknown DLL from %TEMP%] — a common post-exploitation pattern following a font-parsing exploit that drops and executes a shellcode loader.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A remote code execution vulnerability exists in Microsoft Windows when the Windows Adobe Type Manager Library improperly handles a specially-crafted multi-master font - Adobe Type 1 PostScript format.For all systems except Windows 10, an attacker who successfully exploited the vulnerability could execute code remotely, aka 'Adobe Font Manager Library Remote Code Execution Vulnerability'. This CVE ID is unique from CVE-2020-1020.

    Source: schneider_csaf, NVD (NIST), cvelistv5, CISA KEV Catalog

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    VendorProductAffected versionsFixed in
    MicrosoftWindows
    • 10 Version 1803 for x64-based Systems
    • 10 Version 1709 for ARM64-based Systems
    • RT 8.1
    • 10 Version 1809 for ARM64-based Systems
    • 10 Version 1709 for x64-based Systems
    • 10 for 32-bit Systems
    • 8.1 for 32-bit systems
    • 10 for x64-based Systems
    • 10 Version 1803 for 32-bit Systems
    • 10 Version 1607 for 32-bit Systems
    • 7 for x64-based Systems Service Pack 1
    • 10 Version 1607 for x64-based Systems
    • 7 for 32-bit Systems Service Pack 1
    • 10 Version 1809 for x64-based Systems
    • 10 Version 1809 for 32-bit Systems
    • 8.1 for x64-based systems
    • 10 Version 1709 for 32-bit Systems
    • 10 Version 1803 for ARM64-based Systems
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    MicrosoftWindows Server
    • 2008 for Itanium-Based Systems Service Pack 2
    • 2012 R2
    • 2019
    • 2008 for x64-based Systems Service Pack 2 (Core installation)
    • 2008 R2 for x64-based Systems Service Pack 1
    • 2012 (Core installation)
    • 2008 for 32-bit Systems Service Pack 2 (Core installation)
    • 2008 for 32-bit Systems Service Pack 2
    • 2008 R2 for Itanium-Based Systems Service Pack 1
    • 2012
    • 2012 R2 (Core installation)
    • 2019 (Core installation)
    • 2008 R2 for x64-based Systems Service Pack 1 (Core installation)
    • 2016 (Core installation)
    • 2016
    • version 1803 (Core Installation)
    • 2008 for x64-based Systems Service Pack 2
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    Schneider ElectricMicrosoft Windows
    • 10
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    Vendors and products

    Affected operating systems

    Affected operating systems
    FamilyVendorProductVersion
    Windowsmicrosoftwindows_10_1507—
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_1709—
    Windowsmicrosoftwindows_10_1803—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_10_1903—
    Windowsmicrosoftwindows_10_1909—
    Windowsmicrosoftwindows_7—
    Windowsmicrosoftwindows_8.1—
    Windowsmicrosoftwindows_rt_8.1—
    Windowsmicrosoftwindows_server_1803—
    Windowsmicrosoftwindows_server_1903—
    Windowsmicrosoftwindows_server_1909—
    Windowsmicrosoftwindows_server_2008r2
    Windowsmicrosoftwindows_server_2008—
    Windowsmicrosoftwindows_server_2012r2
    Windowsmicrosoftwindows_server_2012—
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_2019—

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    SourceReferenceMaturityPublished
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2020-ALE-009 – Multiples vulnérabilités dans Microsoft Windows (clôturée 2020-06-23) (opens in a new tab)cert.cyber.gouv.fractively exploited
    Packet StormApple CoreText libFontParser.dylib Stack Corruption (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2020-0938x_refsource_MISC, Patch, Vendor advisory
    • packetstormsecurity.comfiles/161299/Apple-CoreText-libFontParser.dylib-Stack-Corruptio…x_refsource_MISC, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0938government-resource, US government resource
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2020-ALE-009 – Multiples vulnérabilités dans Microsoft Windows (clôturée 2020-06-23)cert-fr
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    <a href="https://intel.neosec.eu/en/cve/CVE-2020-0938"><img src="https://intel.neosec.eu/badge/cve/CVE-2020-0938.svg?lang=en" alt="CVE-2020-0938 – NEOSEC Intel" height="20"></a>