CVE-2021-30753 in iOS
Summary
by MITRE • 09/08/2021
Processing a maliciously crafted font may result in the disclosure of process memory. This issue is fixed in macOS Big Sur 11.4, tvOS 14.6, watchOS 7.5, iOS 14.6 and iPadOS 14.6. An out-of-bounds read was addressed with improved input validation.
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Analysis
by VulDB Data Team • 09/11/2021
The vulnerability identified as CVE-2021-30753 represents a critical memory safety issue within Apple's font processing subsystem that affects multiple operating systems including macOS Big Sur, tvOS, watchOS, iOS, and iPadOS. This flaw resides in the way the system handles font files, specifically when processing maliciously crafted font data that could trigger unintended memory access patterns. The vulnerability manifests as an out-of-bounds read condition that occurs during font parsing operations, where the application fails to properly validate font data boundaries before accessing memory locations. This type of vulnerability falls under the CWE-129 category of Improper Validation of Array Index, which directly relates to the lack of proper input validation mechanisms in the font processing pipeline. The issue demonstrates a classic memory corruption vulnerability pattern where untrusted font data can cause the application to read memory beyond the intended buffer boundaries.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides potential attackers with access to sensitive process memory contents that may contain confidential data, cryptographic keys, or system credentials. When an application processes a malicious font file, the out-of-bounds read operation can expose memory regions that should remain protected, potentially allowing attackers to extract information that could be used for further exploitation or system compromise. The vulnerability affects Apple's Core Text framework which is responsible for font rendering across all supported platforms, making it a widespread concern that impacts numerous applications that rely on standard font processing. Attackers could potentially leverage this vulnerability through various attack vectors including email attachments, web content, or malicious documents that contain crafted font files, making it particularly dangerous in environments where users frequently interact with untrusted content.
Security researchers have identified that the fix implemented by Apple addresses this issue through enhanced input validation mechanisms that properly bounds-check font data before processing. The mitigation strategy involves strengthening the font parsing logic to prevent out-of-bounds memory access by implementing proper validation of font file structures and ensuring that all array indices and memory access operations remain within defined boundaries. This remediation approach aligns with the ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript, as attackers who successfully exploit such vulnerabilities could potentially use the memory disclosure to gain additional information about system state or application memory layout. The vulnerability also relates to the broader category of privilege escalation attacks where initial access through font processing could lead to more severe compromise scenarios. Organizations should prioritize patching affected systems to prevent exploitation, as the vulnerability could be leveraged in targeted attacks against specific users or organizations where attackers craft malicious fonts designed to exploit this specific memory access flaw. The fix demonstrates Apple's commitment to addressing memory safety issues through proactive security measures that prevent unauthorized memory access patterns while maintaining system stability and user experience across all supported platforms.