CVE-2020-29624 in tvOS
Summary
by MITRE • 04/03/2021
A memory corruption issue existed in the processing of font files. This issue was addressed with improved input validation. This issue is fixed in watchOS 7.2, macOS Big Sur 11.1, Security Update 2020-001 Catalina, Security Update 2020-007 Mojave, iOS 14.3 and iPadOS 14.3, tvOS 14.3. Processing a maliciously crafted font file may lead to arbitrary code execution.
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Analysis
by VulDB Data Team • 04/08/2021
The vulnerability identified as CVE-2020-29624 represents a critical memory corruption flaw that affects the processing of font files across multiple Apple operating systems. This issue resides in the core font handling mechanisms that interpret and render various font formats including TrueType, OpenType, and other proprietary font types. The flaw stems from insufficient input validation during the parsing of font metadata, specifically within the font rendering engine that translates font instructions into visual representations on screen. Such memory corruption vulnerabilities are particularly dangerous because they can be triggered through seemingly benign operations like displaying text or rendering user interfaces that utilize affected font files. The vulnerability manifests when the system encounters malformed or maliciously crafted font data that bypasses normal validation checks, leading to unpredictable memory state changes that can be exploited by attackers.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions that can lead to memory corruption and arbitrary code execution. The flaw operates at the intersection of font processing and memory management, where improper bounds checking allows attackers to manipulate memory layout through carefully constructed font files. This type of vulnerability is categorized under the ATT&CK technique T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1068 for "Exploitation for Privilege Escalation" when considering the potential for privilege escalation through successful exploitation. The memory corruption occurs during the font parsing phase where the system attempts to load font metrics, glyph data, and rendering instructions without adequate safeguards against malformed input sequences that could overwrite adjacent memory regions.
The operational impact of CVE-2020-29624 extends across Apple's entire ecosystem including iOS, macOS, watchOS, and tvOS platforms, making it a widespread concern for organizations relying on Apple devices. Attackers could exploit this vulnerability by delivering malicious font files through various attack vectors including email attachments, web downloads, or malicious websites that render font-based content. The potential for arbitrary code execution means that successful exploitation could result in complete system compromise, allowing attackers to install persistent backdoors, exfiltrate sensitive data, or establish command and control channels. The vulnerability is particularly concerning because font files are frequently encountered in legitimate user activities, making it difficult to distinguish between benign and malicious content without proper input validation. Organizations should consider this vulnerability as a high-priority threat that could enable advanced persistent threats targeting Apple environments.
Mitigation strategies for CVE-2020-29624 focus on applying the available security updates from Apple that implement improved input validation and memory safety mechanisms. The patched versions include watchOS 7.2, macOS Big Sur 11.1, Security Update 2020-001 for Catalina, Security Update 2020-007 for Mojave, and iOS 14.3 with iPadOS 14.3 and tvOS 14.3. System administrators should prioritize deployment of these updates across all affected devices to eliminate the risk of exploitation. Additional protective measures include implementing network-level filtering to block suspicious font file downloads, enabling sandboxing mechanisms for font processing, and conducting regular security assessments to identify potentially compromised systems. Organizations should also consider implementing monitoring solutions that can detect unusual font processing activities or memory access patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of robust input validation in font rendering systems and highlights the need for continuous security testing of core operating system components that handle user-supplied content.