CVE-2020-9901 in tvOS
Summary
by MITRE • 10/23/2020
An issue existed within the path validation logic for symlinks. This issue was addressed with improved path sanitization. This issue is fixed in iOS 13.6 and iPadOS 13.6, macOS Catalina 10.15.6, tvOS 13.4.8. A local attacker may be able to elevate their privileges.
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Analysis
by VulDB Data Team • 10/03/2022
The vulnerability identified as CVE-2020-9901 represents a critical path validation flaw within Apple's operating systems that affects iOS 13.5 and earlier versions, iPadOS 13.5 and earlier, macOS Catalina 10.15.5 and earlier, and tvOS 13.4.7 and earlier. This issue resides in the symlink path validation logic, which serves as a fundamental security mechanism for managing symbolic link resolution within the file system. The flaw stems from inadequate sanitization of path components when processing symbolic links, creating potential pathways for malicious exploitation. The vulnerability falls under CWE-22 which specifically addresses Improper Limitation of a Pathname to a Restricted Directory, commonly known as Path Traversal, and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter. The affected systems implement a sophisticated file system security model that relies on proper path validation to prevent unauthorized access to restricted directories and system resources.
The technical implementation of this vulnerability occurs when the operating system processes symbolic links without sufficient validation of the path components, allowing attackers to craft malicious symlink structures that can bypass normal access controls. When a symlink is created or resolved, the system should validate that the target path remains within acceptable boundaries and does not reference restricted locations or attempt to traverse outside of designated directories. However, the flawed validation logic permits certain path sequences that should be rejected, potentially allowing attackers to create symlinks that point to privileged locations or directories that should be inaccessible to regular users. This weakness is particularly concerning because it operates at the kernel level where the system maintains the integrity of its access control mechanisms and where the distinction between user and system privileges is most critical. The vulnerability enables an attacker to manipulate the path resolution process in such a way that subsequent operations on the symlink may be interpreted as originating from privileged contexts rather than the attacker's user account.
The operational impact of this vulnerability is significant as it provides a local privilege escalation vector that could allow a malicious user or application with standard user privileges to gain elevated access to system resources. When exploited successfully, this vulnerability could enable attackers to access sensitive system files, modify critical system components, or potentially gain root-level access to the affected device. The implications extend beyond simple file access, as the ability to bypass path validation mechanisms can compromise the entire integrity of the system's security model, particularly in environments where multiple users or applications interact with the file system. This vulnerability directly undermines the principle of least privilege that forms the foundation of modern operating system security models. Attackers could leverage this weakness to escalate their privileges and perform actions that should normally be restricted to system administrators or privileged processes, potentially leading to complete system compromise and data exfiltration.
Apple addressed this vulnerability through enhanced path sanitization mechanisms that properly validate symlink target paths before allowing their resolution. The fix implemented in iOS 13.6, iPadOS 13.6, macOS Catalina 10.15.6, and tvOS 13.4.8 includes improved validation routines that rigorously check path components against established security boundaries and reject any sequences that could potentially lead to privilege escalation. The mitigation strategy involves strengthening the symlink resolution logic to ensure that all path components are properly validated and that symbolic links cannot be used to traverse outside of designated safe zones within the file system hierarchy. Organizations should immediately deploy these security updates to protect their systems from exploitation attempts, as the vulnerability exists in all versions prior to the patched releases. The fix aligns with security best practices outlined in the NIST Cybersecurity Framework and represents a critical defensive measure against local privilege escalation attacks that could otherwise be used to compromise entire device ecosystems. System administrators should verify that all affected devices have been updated to the patched versions and monitor for any potential exploitation attempts that may have occurred before the patch was deployed.