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

CVE-2020-0938 is a remote code execution vulnerability in the Microsoft Windows Adobe Font Manager Library. It arises when the library processes specially crafted multi-master fonts in Adobe Type 1 PostScript format. Successful exploitation can allow an attacker to run code on affected Windows systems; on Windows 10 the resulting code runs inside an AppContainer sandbox with limited privileges, while on other Windows versions the impact is broader remote code execution. IT and security teams should treat this as a high-priority font-handling flaw because fonts are commonly embedded in documents and web content that users open in the course of normal work.

Public detail is limited to the CISA description and the stated CWE. Confirm exact affected builds, patch identifiers, and any additional constraints directly against the Microsoft vendor advisory before acting.

How it works

The weakness is classified as CWE-787 (out-of-bounds write). In this class of flaw, software writes data past the end or before the beginning of an intended buffer. When the Adobe Font Manager Library parses a maliciously formed multi-master Type 1 font, the out-of-bounds write can corrupt memory in a way that lets an attacker influence control flow and achieve code execution.

An attacker would typically deliver the crafted font inside a document, email attachment, or other content that triggers the library. Once the font is processed, the memory corruption occurs. On non-Windows 10 systems the result can be full remote code execution; on Windows 10 the same flaw is constrained to an AppContainer sandbox, reducing but not eliminating the attacker’s capabilities. No further exploit mechanics are provided in the available facts; treat any public proof-of-concept claims with caution and validate them only against official vendor information.

Am I affected? How to find it in your systems

The vulnerability affects Microsoft Windows systems that include the Adobe Font Manager Library. This component is part of the operating system’s font-handling stack and is present on typical desktop and server installations that process documents or web content containing Type 1 fonts.

• Inventory all Windows endpoints and servers; group them by major version (especially distinguishing Windows 10 from earlier releases) because the sandboxing outcome differs.
• Confirm the presence of the Adobe Font Manager Library and the installed OS build against the version ranges listed in the Microsoft advisory; do not rely on informal version lists.
• Review software distribution and patch-management inventories for any systems that have not yet received the corresponding security update.
• Look for telemetry that indicates unusual font parsing activity, crashes in font-related processes, or unexpected child processes spawned after a user opens a document. Such signals are generic for this class of flaw and must be correlated with the specific advisory guidance.

If your environment still processes Adobe Type 1 or multi-master fonts from untrusted sources, treat those systems as higher priority for verification.

How to remediate

The primary remediation is to apply the security updates Microsoft released for this vulnerability. Follow the vendor instructions exactly; CISA’s required action is simply “Apply updates per vendor instructions.”

• Deploy the relevant Windows security update through your normal patch channel (WSUS, ConfigMgr, Intune, or manual installation) after testing in a representative pilot group.
• Verify installation by checking the update history or build/revision numbers against the advisory.
• After patching, reboot if the advisory requires it, then confirm the library no longer exhibits the vulnerable behavior.
• As hardening for the broader out-of-bounds-write class, keep the OS and all font-consuming applications current, and prefer modern font formats over legacy Type 1 fonts where business needs allow.

If you can't patch immediately

When immediate patching is not possible, apply compensating controls that reduce exposure to malicious fonts and limit post-exploitation impact.

• Segment high-risk user workstations from critical servers and restrict outbound connections from those workstations until they are patched.
• Use application control or Attack Surface Reduction rules to block untrusted Office macros and to constrain processes that load fonts.
• If a web application firewall or endpoint protection platform offers virtual-patching signatures for this CVE or for Type 1 font parsing anomalies, enable them after validating they do not break legitimate traffic.
• Disable or restrict the handling of Adobe Type 1 / multi-master fonts where the business can tolerate the loss of compatibility; confirm the exact configuration steps in Microsoft documentation.
• Increase monitoring for font-related process crashes, unexpected code injection, and sandbox escapes, and alert on any anomalous child-process creation following document opens.

These measures lower risk but do not replace the vendor patch.

If your data may have been exposed

Actively exploited remote-code-execution vulnerabilities can lead to follow-on compromise and data theft. Known ransomware use of this specific CVE is not documented in the provided facts. If you have reason to believe systems were exploited before patching, follow your incident-response plan: isolate affected hosts, preserve forensic evidence, and assess whether credentials or data left the environment. As a simple additional check, users can run a free exposure scan of their work email addresses against known breach data sets to see whether those addresses already appear in public breach corpora.