CVE-2020-1020
Microsoft Windows Adobe Font Manager Library Remote Code Execution Vulnerability
Description
CVE-2020-1020 is a HIGH-severity remote code execution vulnerability in the Microsoft Windows Adobe Font Manager Library with a CVSS 3.1 score of 8.8. This vulnerability is closely related to CVE-2020-0938 and exists when the Windows Adobe Type Manager Library improperly handles specially crafted multi-master fonts in Adobe Type 1 PostScript format. For systems other than Windows 10, successful exploitation allows full remote code execution. On Windows 10, exploitation is constrained to an AppContainer sandbox with limited privileges. Affected products span Windows 7 through Windows 10 and Windows Server 2008 through 2019. This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of 2022-05-03. The EPSS score of 0.87956 (99.48th percentile) indicates extremely high exploitation probability.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | - |
| microsoft | windows 10 1607 | - |
| microsoft | windows 10 1709 | - |
| microsoft | windows 10 1803 | - |
| microsoft | windows 10 1809 | - |
| microsoft | windows 10 1903 | - |
| microsoft | windows 10 1909 | - |
| microsoft | windows 7 | - |
| microsoft | windows 8.1 | - |
| microsoft | windows rt 8.1 | - |
| microsoft | windows server 1903 | - |
| microsoft | windows server 1909 | - |
| microsoft | windows server 2008 | -; r2 |
| microsoft | windows server 2012 | -; r2 |
| microsoft | windows server 2016 | - |
| microsoft | windows server 2019 | - |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1020(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-1020(US Government Resource)
Weakness Type
CWE-787: Out-of-bounds Write
CVE-2020-1020 is classified under CWE-787 — Out-of-bounds Write. This weakness occurs when software writes data past the boundary of an allocated buffer, corrupting adjacent memory. Out-of-bounds writes can overwrite function pointers, return addresses, and critical data structures, enabling arbitrary code execution.
In the context of the Windows Adobe Font Manager Library, this out-of-bounds write occurs during parsing of malformed Adobe Type 1 PostScript multi-master font data. The font rendering subsystem is a particularly sensitive attack surface because font processing happens automatically across many Windows components including document viewers, web browsers, and the Windows Explorer shell.
Learn more: CWE-787 — Out-of-bounds Write
Impact Analysis
CVE-2020-1020 carries a CVSS 3.1 score of 8.8 (HIGH) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation grants the attacker full access to data processed by the compromised application. On pre-Windows 10 systems, this extends to all user-accessible data including credentials, documents, and network resources.
Integrity (HIGH): Attackers can install persistent malware, modify system files, alter security configurations, and deploy backdoors for long-term access.
Availability (HIGH): Exploitation can cause application crashes, system instability, or denial of service through malicious font processing. Attackers with code execution can also intentionally disrupt system operations.
Scope Unchanged: On Windows 10, impact is mitigated by the AppContainer sandbox. On older Windows versions, the attacker gains the full privileges of the process that renders the font, which may include user-level or service-level access.
With an EPSS score of 0.87956 (99.48th percentile), this vulnerability is among the most likely to be exploited across all tracked vulnerabilities.
Exploit Maturity
CVE-2020-1020 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.
Exploit status: This vulnerability was exploited as a zero-day alongside CVE-2020-0938 before patches were available. Microsoft acknowledged limited targeted attacks in March 2020. The EPSS score of 0.87956 (99.48th percentile) confirms extremely high real-world exploitation activity.
Ransomware association: No direct ransomware association has been confirmed per KEV data. However, the ability to achieve remote code execution through document-based attacks makes this vulnerability suitable for initial access in ransomware campaigns.
Attack surface: Similar to CVE-2020-0938, the vulnerability can be triggered by opening a malicious document, previewing a file in Windows Explorer, or browsing to a webpage with crafted font content. The network attack vector (CVSS AV:N) with no privilege requirements significantly broadens the potential attack surface.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2022-05-03.
Remediation
- Apply Microsoft security updates immediately. Install the April 2020 security updates per Microsoft's advisory at portal.msrc.microsoft.com.
- Identify all affected systems. Inventory all Windows 7, 8.1, 10, RT 8.1, and Windows Server 1903 through 2019 instances. Systems running pre-Windows 10 versions require highest priority.
- Disable the Windows Explorer Preview Pane. As an interim mitigation, disable both the Preview Pane and Details Pane in Windows Explorer to prevent automatic font rendering that can trigger exploitation.
- Disable the WebClient service. Disable WebDAV to reduce the remote attack surface and prevent exploitation through network-based font delivery.
- Rename the ATMFD.DLL library. As an additional interim measure, renaming or disabling the Adobe Type Manager Font Driver library (ATMFD.DLL) prevents the vulnerable code from executing, though this may affect Type 1 font rendering.
- Monitor and scan for compromise indicators. Review system logs for evidence of exploitation and conduct security scans targeting indicators associated with font-based attacks. Prioritize migration from end-of-life Windows versions.
Technical Details
CVE-2020-1020 is a HIGH-severity remote code execution vulnerability that can be exploited over the network with low attack complexity. No privileges are required, but user interaction is necessary.
Technical mechanism: The vulnerability exists in the Windows Adobe Type Manager Library (atmfd.dll), which processes Adobe Type 1 PostScript fonts. When parsing specially crafted multi-master font data, the library fails to properly validate font metrics, triggering an out-of-bounds write that corrupts heap memory. An attacker can structure the malicious font to control the memory corruption and achieve code execution in the context of the rendering process.
Relationship to CVE-2020-0938: Both CVE-2020-1020 and CVE-2020-0938 target the same vulnerable component (atmfd.dll) with similar exploitation techniques. They represent distinct code paths that lead to the same class of vulnerability. Both were exploited in the wild before patches were available.
CVSS 3.1 vector analysis: AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H — The network attack vector and lack of privilege requirements make this more broadly exploitable than local-only vulnerabilities. The user interaction requirement means the victim must open a document or visit a webpage.
Affected products: Windows 10 (1507 through 1909), Windows 7, Windows 8.1, Windows RT 8.1, and Windows Server 1903 through 2019.
Frequently Asked Questions
Is CVE-2020-1020 being actively exploited?
Yes, CVE-2020-1020 has been actively exploited as a zero-day alongside CVE-2020-0938. Microsoft confirmed limited targeted attacks before releasing patches in April 2020. The EPSS score of 0.87956 (99.48th percentile) confirms extremely high exploitation probability, and the vulnerability is listed in CISA's KEV catalog.
Which products are affected by CVE-2020-1020?
CVE-2020-1020 affects Microsoft Windows products including Windows 7, Windows 8.1, Windows 10 (builds 1507 through 1909), Windows RT 8.1, and Windows Server versions 1903, 1909, 2008, 2012, 2016, and 2019. Systems running pre-Windows 10 are at highest risk due to the lack of AppContainer sandboxing.
How do I fix CVE-2020-1020?
Apply the April 2020 security updates from Microsoft. As interim mitigations, disable the Preview Pane and Details Pane in Windows Explorer, disable the WebClient service, and consider renaming ATMFD.DLL. Prioritize migration from end-of-life operating systems like Windows 7.
How severe is CVE-2020-1020?
CVE-2020-1020 is rated HIGH with a CVSS 3.1 score of 8.8 and a network attack vector. On non-Windows 10 systems, exploitation achieves full remote code execution without any sandbox restrictions. The EPSS score of 0.87956 (99.48th percentile) places it among the most actively exploited vulnerabilities tracked globally.
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