CVE-2020-27930: Apple iPadOS Font Parsing RCE Vulnerability

CVE-2020-27930 Overview

CVE-2020-27930 is a memory corruption vulnerability affecting multiple Apple operating systems including macOS, iOS, iPadOS, and watchOS. The vulnerability exists in the font parsing functionality and can be triggered when processing a maliciously crafted font file. Successful exploitation allows an attacker to execute arbitrary code with the privileges of the targeted application.

This vulnerability is particularly significant as it has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. The vulnerability was addressed by Apple through improved input validation in the font processing subsystem.

Critical Impact

This is a known exploited vulnerability listed in CISA's KEV catalog. Processing a maliciously crafted font can lead to arbitrary code execution across Apple's entire ecosystem including macOS, iOS, iPadOS, and watchOS devices.

Affected Products

• Apple macOS (Big Sur 11.0.1, Catalina 10.15.7, High Sierra, Mojave)
• Apple iOS 12.4.9, iOS 14.2 and iPadOS 14.2
• Apple watchOS 5.3.9, watchOS 6.2.9, watchOS 7.1

Discovery Timeline

• 2020-12-08 - CVE-2020-27930 published to NVD
• 2025-10-27 - Last updated in NVD database

Technical Details for CVE-2020-27930

Vulnerability Analysis

CVE-2020-27930 is classified as CWE-787 (Out-of-Bounds Write), a memory corruption vulnerability that occurs during font file parsing operations. The flaw exists in how Apple's operating systems handle specially crafted font data, where malicious input can cause memory to be written beyond the bounds of an allocated buffer.

The vulnerability affects the core font rendering subsystem shared across Apple's product line, which explains the wide range of affected products spanning desktop, mobile, and wearable platforms. When a maliciously crafted font is processed—whether through web content, email attachments, documents, or other vectors that render fonts—the out-of-bounds write can corrupt adjacent memory structures.

This memory corruption can be leveraged by attackers to achieve arbitrary code execution. The local attack vector with user interaction required indicates that exploitation typically requires convincing a victim to open a document or visit a website containing the malicious font. The fact that this vulnerability was exploited in the wild and added to CISA's Known Exploited Vulnerabilities catalog underscores its severity and practical exploitability.

Root Cause

The root cause of CVE-2020-27930 is insufficient input validation in the font parsing code. When processing font file data, the parser failed to properly validate input boundaries before performing write operations. This allows specially crafted font data to trigger an out-of-bounds write condition, corrupting memory in a controllable manner.

Apple addressed this issue by implementing improved input validation in the font processing routines, ensuring that font data is properly sanitized before memory operations are performed.

Attack Vector

The attack vector for CVE-2020-27930 is local with user interaction required. An attacker must deliver a maliciously crafted font file to the victim system, which can be accomplished through several means:

1. Web-based delivery - Embedding malicious fonts in web pages that victims visit
2. Document-based delivery - Including malicious fonts in documents (PDFs, Word documents, etc.)
3. Email attachments - Sending files containing malicious font data
4. Messaging applications - Sharing content that triggers font rendering

When the victim's system processes the malicious font through any application that utilizes system font rendering, the out-of-bounds write is triggered, potentially leading to arbitrary code execution within the context of the affected process.

According to Packet Storm Security, exploitation techniques for this vulnerability have been documented in the wild.

Detection Methods for CVE-2020-27930

Indicators of Compromise

• Unexpected crashes in font rendering processes or applications handling document/web content
• Suspicious font files with unusual sizes or malformed headers being accessed
• Anomalous memory access patterns in processes that handle font rendering
• Crash reports indicating memory corruption in font-related system libraries

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions capable of monitoring memory corruption attacks
• Implement file integrity monitoring for system font directories and font cache locations
• Monitor for suspicious process behavior following document or web content access
• Utilize exploit detection capabilities that can identify out-of-bounds memory operations

Monitoring Recommendations

• Enable crash reporting and analysis to identify potential exploitation attempts
• Monitor network traffic for delivery of suspicious document types or web content
• Implement logging for font file access and rendering operations where possible
• Correlate endpoint telemetry with threat intelligence feeds for known exploitation indicators

How to Mitigate CVE-2020-27930

Immediate Actions Required

• Update all Apple devices to the patched versions immediately as this is a known exploited vulnerability
• Prioritize patching for devices that handle external content such as emails, web browsing, or documents
• Restrict access to untrusted documents and web content until patches are applied
• Enable automatic updates on all Apple devices to ensure timely security patch deployment

Patch Information

Apple has released security updates addressing CVE-2020-27930 across multiple product lines. Administrators should apply the following updates:

• macOS: Big Sur 11.0.1, Catalina 10.15.7 Supplemental Update, Security Update 2020-006 for High Sierra and Mojave
• iOS/iPadOS: iOS 12.4.9, iOS 14.2, iPadOS 14.2
• watchOS: watchOS 5.3.9, watchOS 6.2.9, watchOS 7.1

Detailed patch information is available through Apple's security advisories:

• Apple Security Update HT211928
• Apple Security Update HT211929
• Apple Security Update HT211931
• Apple Security Update HT211940
• Apple Security Update HT211944
• Apple Security Update HT211945
• Apple Security Update HT211946
• Apple Security Update HT211947

Workarounds

• Limit exposure to untrusted content sources until patches can be applied
• Implement network-level filtering to block known malicious content delivery mechanisms
• Use mobile device management (MDM) solutions to enforce security policies and restrict app installations
• Disable automatic font downloads in browsers where supported as a temporary measure
• Consider network segmentation to limit the impact of potential compromises

# Verify macOS system version to confirm patch status
sw_vers -productVersion

# Check for pending macOS security updates
softwareupdate --list

# Install available macOS security updates
sudo softwareupdate --install --all