CVE-2020-27930: Apple Multiple Products Memory Corruption Vulnerability

CVE-2020-27930 is a memory corruption vulnerability in the FontParser component of Apple iOS, iPadOS, macOS, and watchOS. Processing a maliciously crafted font can allow an attacker to achieve code execution on the device. This matters because fonts are routinely handled by the operating system during everyday activities such as viewing documents or web content, giving the flaw a practical path into user and enterprise devices if left unpatched.

CISA lists the required action as applying updates per vendor instructions. Ransomware use is not documented for this CVE. Confirm all product-specific details against the official Apple advisory.

How it works

The weakness is classified as CWE-787 (out-of-bounds write). FontParser fails to handle certain malformed font data safely, resulting in memory corruption. An attacker who can supply a crafted font file—commonly delivered through a document, web page, or other content the device will parse—can trigger the corruption. Successful exploitation may allow arbitrary code execution in the context of the vulnerable process.

Exact exploit mechanics, required user interaction, and privilege levels are not detailed in the provided facts; treat any public proof-of-concept claims cautiously and validate against the vendor advisory. The core risk is that font parsing is a common, often automatic operation, so the attack surface is broader than features users consciously enable.

Am I affected? How to find it in your systems

The vulnerability affects Apple iOS, iPadOS, macOS, and watchOS systems that include the vulnerable FontParser component. These platforms appear on phones, tablets, laptops, desktops, and watches used by employees and in managed fleets.

• Inventory Apple devices via MDM (Jamf, Intune, Kandji, etc.), Apple Business Manager, or endpoint management consoles. Record OS version and build for every device.
• Compare collected versions against the fixed releases listed in Apple’s security advisory for CVE-2020-27930. Do not rely on generic version ranges; confirm the exact builds Apple identifies as patched.
• On macOS, review installed applications and document viewers that embed or invoke system font handling. On mobile devices, note any unmanaged or personally enrolled devices that may lag behind corporate update policies.
• Telemetry signs of exploitation are not specified in the given facts. In general for this class, monitor for unexpected process crashes in font-related or rendering components, anomalous code-signing failures, or sudden privilege escalations following document or web content open events. Forward unified logs and crash reports to your SIEM and baseline normal FontParser behavior where possible.

If your inventory tooling cannot query OS build levels, treat devices that have not received recent Apple security updates as potentially exposed until verified.

How to remediate

Patch first. Apply the security updates Apple released for the affected products, following the vendor’s instructions exactly. Use MDM or automated update mechanisms to drive installation and verify successful application via version inventory.

• Prioritize internet-facing and high-value user devices, then complete fleet-wide rollout.
• After patching, re-scan to confirm the fixed builds are present.
• For defense-in-depth against memory-corruption bugs in parsers: keep additional Apple security features enabled (system integrity protections, hardened runtime where applicable), limit installation of untrusted fonts or font-management tools, and restrict document sources when feasible.
• Ensure crash reporting and endpoint detection are active so residual exploitation attempts surface quickly.

Confirm the precise update names and build numbers in Apple’s advisory; do not assume a generic “latest OS” status is sufficient without checking.

If you can't patch immediately

Implement compensating controls while you schedule the update:

• Segment vulnerable devices from sensitive networks and crown-jewel assets; apply stricter egress filtering.
• Use web and email gateways to block or sandbox attachments and content types most likely to carry crafted fonts (documents, archives, untrusted web fonts) where policy allows.
• If a virtual-patching or IPS signature exists for this CVE from your security vendor, enable it after testing; treat it as temporary.
• Disable or restrict non-essential font installation and third-party font managers on macOS until patched.
• Increase monitoring: alert on FontParser or related rendering process crashes, unexpected child processes, and post-crash network connections. Retain device logs for forensic review.
• For high-risk users, consider temporary browser and document-viewer hardening (disable automatic font download, open untrusted files in isolated viewers).

These measures reduce likelihood and impact but do not eliminate the vulnerability; patching remains the definitive fix.

If your data may have been exposed

Actively exploited memory-corruption vulnerabilities can lead to device compromise and subsequent data theft. If you have indicators of exploitation or unpatched devices that handled untrusted content, follow your incident-response process: isolate affected endpoints, preserve logs and memory images, rotate credentials accessible from those devices, and assess what data may have been reachable. Ransomware use is not documented for this CVE, but any code-execution foothold warrants full investigation. You can run a free exposure scan of your email addresses against known breach data sets to check whether associated credentials or personal information have appeared in prior incidents, then force password resets and enable stronger authentication where matches are found.