CVE-2017-13786 in macOS
Summary
by MITRE
An issue was discovered in certain Apple products. macOS before 10.13.1 is affected. The issue involves the "APFS" component. It does not properly restrict the DMA mapping time of FileVault decryption buffers, which allows attackers to read cleartext APFS data via a crafted Thunderbolt adapter.
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Analysis
by VulDB Data Team • 01/05/2023
The vulnerability identified as CVE-2017-13786 represents a critical security flaw in Apple's APFS (Apple File System) implementation affecting macOS versions prior to 10.13.1. This issue specifically targets the FileVault full-disk encryption feature and demonstrates how hardware-level attacks can compromise system security through DMA (Direct Memory Access) vulnerabilities. The flaw exists within the APFS component's handling of decryption buffers during the FileVault decryption process, creating a pathway for unauthorized data access that bypasses traditional encryption mechanisms.
The technical root cause of this vulnerability lies in the improper restriction of DMA mapping time for FileVault decryption buffers. When a system is decrypting data from an encrypted APFS volume, the decryption buffers must be mapped into the system's memory space to facilitate the decryption process. The flaw occurs because the system does not adequately control when these buffers can be accessed via DMA operations, allowing malicious actors to exploit this window of opportunity. This issue is particularly concerning because it leverages the Thunderbolt interface, which supports high-speed DMA operations and can be exploited by attackers who physically access a target system.
The operational impact of CVE-2017-13786 is severe and far-reaching, as it enables attackers to extract cleartext data from encrypted APFS volumes without requiring authentication or knowledge of encryption keys. This attack vector specifically targets systems with FileVault enabled, which is Apple's primary full-disk encryption solution. The vulnerability can be exploited through a crafted Thunderbolt adapter, making it particularly dangerous in environments where physical access to systems is possible. Attackers can potentially extract sensitive data including personal files, corporate information, and system credentials, effectively nullifying the encryption protections that FileVault is designed to provide. This vulnerability directly relates to CWE-116, which addresses improper handling of data buffers and memory management issues.
The attack scenario typically involves an attacker with physical access to a target system who connects a malicious Thunderbolt device. This device can then perform DMA operations to access the decryption buffers that are temporarily mapped into memory during the FileVault decryption process. The timing window for such attacks is limited but sufficient to extract significant amounts of data. This vulnerability aligns with several ATT&CK techniques including T1011, which covers data encryption for ransom, and T1059, covering command and scripting interpreter usage. The threat model is particularly relevant for enterprise environments where systems may be left unattended or where physical security controls are inadequate.
Organizations should immediately update affected systems to macOS 10.13.1 or later to remediate this vulnerability, as Apple released a security update specifically addressing this issue. Additional mitigations include disabling Thunderbolt interfaces when not in use, implementing strict physical security controls, and monitoring for suspicious hardware connections. Security teams should also consider implementing network-based monitoring to detect potential DMA-based attacks and ensure that FileVault encryption is properly configured with appropriate security settings. The vulnerability underscores the importance of considering hardware-level attack vectors in security planning and demonstrates the critical need for comprehensive security controls that address both software and hardware attack surfaces.