CVE-2019-8517 in macOS
Summary
by MITRE
An out-of-bounds read was addressed with improved bounds checking. This issue is fixed in iOS 12.2, macOS Mojave 10.14.4, tvOS 12.2, watchOS 5.2. Processing a maliciously crafted font may result in the disclosure of process memory.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 06/11/2024
The vulnerability identified as CVE-2019-8517 represents a critical out-of-bounds read flaw that was discovered in Apple's font processing libraries. This issue stems from inadequate bounds checking within the system's font handling mechanisms, specifically affecting how the operating system processes font files. The vulnerability manifests when the system encounters a maliciously crafted font file that contains malformed data structures designed to exploit memory access boundaries. The flaw resides in the font rendering engine's inability to properly validate the size and structure of font data before attempting to read from memory locations, creating opportunities for unauthorized memory access patterns.
This vulnerability falls under the CWE-129 category of Improper Validation of Array Index, which is a fundamental weakness in input validation that allows attackers to manipulate array indices to access memory outside of intended boundaries. The technical implementation of this flaw involves the font processing subsystem attempting to read font metadata or glyph information without sufficient validation of the data's integrity or size constraints. When processing font files, the system allocates memory buffers based on expected data sizes, but malicious inputs can cause these buffers to be accessed beyond their allocated boundaries, potentially exposing sensitive process memory contents.
The operational impact of CVE-2019-8517 extends beyond simple memory disclosure, as it can potentially enable more sophisticated attacks within the context of the affected operating systems. Attackers who successfully exploit this vulnerability could gain access to sensitive information stored in the process memory, including cryptographic keys, user credentials, or application data that might be cached in memory. The vulnerability affects multiple Apple platforms including iOS, macOS, tvOS, and watchOS, creating a widespread attack surface that could be leveraged across various device types. This cross-platform nature aligns with ATT&CK technique T1059.007 for Windows Scripting and T1068 for Exploitation for Privilege Escalation, though the specific attack vectors would need to be adapted for Apple's mobile and desktop environments.
The fix for CVE-2019-8517 involved implementing enhanced bounds checking mechanisms within Apple's font processing libraries, specifically addressing how the system validates font file structures before attempting to read from memory locations. The updated implementations ensure that all font data is properly validated against expected size parameters and memory boundaries before any access operations occur. This remediation approach directly addresses the root cause by strengthening input validation controls and implementing proper memory access controls that prevent out-of-bounds read operations. Security professionals should note that this vulnerability represents a classic example of how font processing libraries can serve as attack vectors due to their complex data structures and the need for extensive validation of potentially untrusted input data from external sources.