CriticalCVE-2020-1020

    Microsoft Windows Adobe Font Manager Library Remote Code Execution Vulnerability (CVE-2020-1020)

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

    What is affected, what to do

    This vulnerability allows remote code execution (RCE) in the Microsoft Windows Adobe Font Manager Library by mishandling specially crafted multi-master fonts. An attacker can gain full control over all affected Windows systems except Windows 10, where code execution occurs in an AppContainer sandbox with limited privileges. The vulnerability is actively exploited in the wild and is listed in the CISA KEV catalog. Affected products include Windows 10 versions 1507, 1607, 1709, 1803, and 1809. Immediate patching is critical.

    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

    8.8

    Priority

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

    Source: NVD, CVSS v3

    8.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Schneider Electric, CVE.org

    65.0 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.25

    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
    222.80 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
    8.8 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
    8.8
    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
    65.0 %
    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
    99.25
    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 a CVSS v3 score of 8.8 (AV:N/AC:L/PR:N/UI:R) and an EPSS percentile of 99.2 %, this vulnerability sits at the very top of the exploitation-likelihood distribution — the low attack complexity and network-reachable vector mean that a single malicious e-mail attachment or shared network folder is sufficient to trigger the vulnerability with minimal user interaction. On all Windows versions below Windows 10, successful exploitation yields unrestricted remote code execution, making any unpatched legacy host an immediate critical risk; Windows 10 systems are partially mitigated by the AppContainer sandbox but are still in scope. Organisations under NIS2 with mixed Windows estates — particularly those running older OS versions in OT-adjacent or production environments — should treat this as a P1 patch event and complete remediation or compensating isolation within 24 hours. Although CISA has not flagged known ransomware campaign use for this CVE, the extremely high EPSS score reflects sustained real-world exploitation interest that justifies treating it with the same urgency.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Apply the vendor patch immediately: Deploy the April 2020 cumulative updates — KB4550945 (Windows 10 1809), KB4550944 (Windows 10 1803), KB4550929 (Windows 10 1709), KB4550927 (Windows 10 1607), KB4550930 (Windows 10 1507) — across all affected endpoints. Verify patch status in WSUS or MECM before closing the ticket.
      • Prioritise pre-Windows-10 systems: On Windows 7, Windows Server 2008 R2, and Windows 8.1 (potentially in scope even if not listed), exploitation results in full remote code execution with no AppContainer sandbox — patch or isolate these first.
      • Disable the Preview Pane and Details Pane in Windows Explorer: Push a GPO under User Configuration > Administrative Templates > Windows Components > Windows Explorer to disable both panes. This removes the attack surface that requires no explicit file-open action by the user.
      • Stop and disable the WebClient service: Run sc config WebClient start= disabled && net stop WebClient on all endpoints that do not require WebDAV. This blocks UNC/WebDAV-based font delivery, a primary exploit delivery path.
      • Block font file types at the perimeter: Configure the e-mail gateway and web proxy to quarantine or strip attachments and downloads with extensions .otf, .pfb, .pfm, .afm.
      • Network-isolate unpatched systems: Move any Windows host that cannot be patched immediately into a restricted VLAN with no outbound internet access until the patch is applied.

    2. Runbook step 2

      Mitigation layers

      • Disable ATMFD.DLL via registry (Microsoft-recommended workaround): On 32-bit Windows 10: reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows" /v DisableATMFD /t REG_DWORD /d 1 /f. On 64-bit systems, also set the same value under HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows. Be aware this may break rendering in some third-party applications.
      • Block outbound SMB at the perimeter firewall: Drop TCP 445 from workstation subnets to the internet to prevent UNC-path-based font delivery from external servers.
      • Activate IPS signatures: Check your Suricata ruleset (emerging-exploit category) for coverage of anomalous OTF/Type-1 font transfers; request Snort SID coverage for CVE-2020-1020 from your signature vendor if not already present.
      • Enforce application control: Use AppLocker or Windows Defender Application Control (WDAC) to block unexpected child processes spawned from font-rendering contexts (atmfd.dll loader, fontdrvhost.exe).
      • Apply least-privilege to end-user accounts: Ensure no standard user holds local administrator rights — this limits post-exploitation impact if a sandbox escape occurs on Windows 10.
      • Sandbox e-mail attachments: Configure the e-mail gateway to detonate Office documents containing embedded OTF fonts or PostScript data in a sandbox before delivery.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 7 (Image Load): Alert when atmfd.dll or atmlib.dll is loaded by unexpected processes such as outlook.exe, browser processes, or dllhost.exe — Sigma shape: EventID: 7 | ImageLoaded|endswith: 'atmfd.dll' | Image|endswith: '\outlook.exe'.
      • Sysmon EID 1 / Windows Event ID 4688 (Process Creation): Detect child processes (cmd.exe, powershell.exe, wscript.exe) spawned directly by explorer.exe or dllhost.exe shortly after a folder containing font files is accessed — KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "explorer.exe" and FileName in~ ("cmd.exe","powershell.exe","wscript.exe").
      • Network telemetry (Zeek/Suricata): Flag outbound SMB (TCP 445) or WebDAV (TCP 80/443 with PROPFIND method) connections from workstations to external IPs within seconds of a document or folder open event — correlate with Sysmon EID 3 (Network Connection) from explorer.exe.
      • EDR process tree: Any network connection or child-process creation originating from fontdrvhost.exe or from a process with atmfd.dll in its loaded-module list should be treated as a P1 alert — this behaviour has no legitimate baseline.
      • Windows Event ID 1000/1001 (Application Crash): Repeated crashes of explorer.exe or dllhost.exe with atmfd.dll listed as the faulting module may indicate failed or in-progress exploitation — SPL: source="WinEventLog:Application" EventCode IN (1000,1001) Message="*atmfd*".

    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-2020-0938.

    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
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    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
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    Schneider ElectricMicrosoft Windows
    • 10
    • —

    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_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

    References & sources

    • portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2020-1020x_refsource_MISC, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-1020government-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
    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2020-1020
    <a href="https://intel.neosec.eu/en/cve/CVE-2020-1020"><img src="https://intel.neosec.eu/badge/cve/CVE-2020-1020.svg?lang=en" alt="CVE-2020-1020 – NEOSEC Intel" height="20"></a>