CVE-2020-9996 in iOS
Summary
by MITRE • 12/09/2020
A use after free issue was addressed with improved memory management. This issue is fixed in macOS Big Sur 11.0.1, iOS 14.0 and iPadOS 14.0. A malicious application may be able to elevate privileges.
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Analysis
by VulDB Data Team • 12/15/2020
The vulnerability identified as CVE-2020-9996 represents a critical use-after-free flaw that existed within Apple's operating systems, specifically affecting versions prior to the security updates released in macOS Big Sur 11.0.1 and iOS 14.0. This type of vulnerability occurs when a program continues to reference memory locations after they have been freed or deallocated, creating potential exploitation opportunities for malicious actors. The issue was particularly concerning because it could be leveraged by a malicious application to achieve privilege escalation, allowing unauthorized code execution with elevated system privileges. The vulnerability stems from inadequate memory management practices where the system failed to properly track memory references, creating a window of opportunity for attackers to manipulate freed memory segments.
The technical nature of this use-after-free vulnerability places it squarely within CWE-416, which defines the weakness of freeing memory twice or using memory after it has been freed. This particular flaw manifested in Apple's kernel or system-level components where memory allocation and deallocation processes were not adequately synchronized to prevent subsequent access to freed memory regions. Attackers could exploit this by crafting malicious applications that would trigger the vulnerable code path, causing the system to free memory while still maintaining references to it. The operating system's memory management subsystem failed to properly invalidate these references, creating a scenario where attacker-controlled data could be written to the freed memory location and subsequently executed with system privileges.
The operational impact of CVE-2020-9996 extends beyond simple privilege escalation to potentially enable full system compromise by malicious applications. This vulnerability aligns with ATT&CK technique T1068, which describes privilege escalation through local system exploitation, and T1548.001, covering abuse of system permissions. The flaw essentially created a backdoor for attackers to bypass normal security boundaries and gain elevated privileges without requiring user interaction or physical access to the device. Mobile and desktop systems were equally at risk, with iOS, iPadOS, and macOS devices all vulnerable to exploitation through this vector. The vulnerability's exploitation required a malicious application to be installed on the target device, making it particularly dangerous in environments where users might be tricked into installing compromised applications or when applications with legitimate permissions could be manipulated to exploit the flaw.
Apple's resolution of this vulnerability through the release of macOS Big Sur 11.0.1 and iOS 14.0 demonstrates the company's approach to addressing memory management issues through improved memory safety mechanisms. The fix likely involved implementing stricter memory reference tracking, adding additional validation checks before memory deallocation, and ensuring proper invalidation of memory references upon deallocation. Security researchers and system administrators should prioritize deployment of these updates across all affected systems, as the vulnerability could enable attackers to establish persistent access to compromised devices. Organizations should also implement monitoring for suspicious application behavior and maintain awareness of the ATT&CK framework's guidance on detecting privilege escalation techniques that may leverage similar memory corruption vulnerabilities. The remediation approach taken by Apple exemplifies industry best practices for addressing use-after-free vulnerabilities through comprehensive memory management improvements and proper resource lifecycle handling.