CVE-2021-30771 in tvOS
Summary
by MITRE • 03/18/2022
An out-of-bounds write was addressed with improved input validation. This issue is fixed in macOS Big Sur 11.4, iOS 14.6 and iPadOS 14.6, watchOS 7.5, tvOS 14.6. Processing a maliciously crafted font file may lead to arbitrary code execution.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 03/23/2022
The vulnerability identified as CVE-2021-30771 represents a critical out-of-bounds write flaw within Apple's font processing libraries that affects multiple operating systems including macOS, iOS, iPadOS, watchOS, and tvOS. This type of vulnerability falls under the CWE-787 category of out-of-bounds write conditions, where an application attempts to write data beyond the allocated memory boundaries of a buffer. The flaw specifically manifests when the system processes maliciously crafted font files, which are commonly used in digital typography and user interface rendering across Apple's ecosystem. The vulnerability demonstrates the inherent risks associated with font parsing libraries, which are frequently exploited due to their complex nature and widespread usage in graphical applications.
The technical exploitation of this vulnerability occurs through the improper validation of font file inputs during the parsing process. When a malicious font file is loaded, the system's font rendering engine fails to properly validate the size and structure of various font components, leading to memory corruption that can be leveraged for arbitrary code execution. This type of attack vector aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where an attacker could potentially execute malicious code through compromised font processing. The vulnerability's impact is particularly severe because font files are ubiquitous in computing environments, making it challenging to prevent exploitation through simple network-based restrictions. Attackers could deliver malicious fonts through various vectors including email attachments, web downloads, or compromised websites, making this a persistent threat across multiple attack surfaces.
The operational impact of CVE-2021-30771 extends beyond simple code execution to potentially enable full system compromise across Apple's mobile and desktop platforms. The vulnerability affects the core font processing capabilities of Apple's operating systems, which means that exploitation could occur in legitimate applications that render text, including email clients, web browsers, and productivity suites. This makes the attack surface particularly broad and difficult to monitor effectively. The affected systems include macOS Big Sur 11.4, iOS 14.6, iPadOS 14.6, watchOS 7.5, and tvOS 14.6, indicating that the vulnerability spans multiple device types and use cases within Apple's ecosystem. Organizations and individuals using these platforms face significant risk without proper patch management, as the vulnerability could be exploited to gain unauthorized access to sensitive information or establish persistent backdoors on affected devices.
Apple's resolution of this vulnerability through software updates demonstrates the importance of proper input validation and memory safety practices in system libraries. The fix implemented in the patched versions addresses the root cause by introducing enhanced validation mechanisms for font file parsing, ensuring that buffer boundaries are properly enforced during memory operations. This remediation approach aligns with security best practices outlined in the CERT/CC Secure Coding Standards, which emphasize the critical importance of bounds checking in memory management operations. Organizations should prioritize immediate deployment of the security patches across all affected Apple platforms to mitigate the risk of exploitation. Additionally, defensive measures such as monitoring for unusual font file processing activity and implementing application sandboxing can provide additional layers of protection against potential exploitation attempts. The vulnerability serves as a reminder of the ongoing importance of maintaining up-to-date security patches and the potential consequences of failing to address memory safety issues in widely-used system components.