CVE-2018-6920 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.1-STABLE(r332303), 11.1-RELEASE-p10, 10.4-STABLE(r332321), and 10.4-RELEASE-p9, due to insufficient initialization of memory copied to userland in the Linux subsystem and Atheros wireless driver, small amounts of kernel memory may be disclosed to userland processes. Unprivileged authenticated local users may be able to access small amounts of privileged kernel data.
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Analysis
by VulDB Data Team • 02/03/2020
The vulnerability described in CVE-2018-6920 represents a critical information disclosure flaw within the FreeBSD operating system's kernel memory management mechanisms. This vulnerability specifically affects versions prior to the mentioned stable and release branches, creating a security gap that allows unprivileged authenticated users to potentially access sensitive kernel memory contents. The issue manifests through two primary attack vectors: the Linux subsystem and the Atheros wireless driver, both of which demonstrate inadequate memory initialization practices when transferring data to userland processes. The flaw stems from insufficient zero-initialization of memory buffers before copying kernel data to user-space, creating potential information leakage pathways that could expose privileged system information to malicious users.
The technical implementation of this vulnerability involves memory management procedures where kernel data structures are copied to userland without proper sanitization of memory contents. When the Linux subsystem or Atheros wireless driver handle data transfers, they fail to adequately initialize memory regions that subsequently get exposed to user processes. This creates a scenario where residual kernel data, potentially containing sensitive information such as cryptographic keys, system credentials, or internal kernel state information, may be inadvertently disclosed to unprivileged processes. The vulnerability is particularly concerning because it operates at the kernel level and leverages legitimate system interfaces, making detection more challenging and exploitation relatively straightforward for authenticated attackers.
From an operational impact perspective, this vulnerability enables local privilege escalation attacks by allowing unprivileged users to gather sensitive kernel information that could be used for further exploitation. The disclosed kernel memory fragments, while small in size, could contain critical information such as memory addresses, kernel configuration details, or other system state data that would aid attackers in crafting more sophisticated attacks. The vulnerability affects the fundamental security model of the operating system by creating unexpected data leakage channels that bypass normal access controls. Security researchers have categorized this issue under CWE-200, which specifically addresses "Information Exposure," and the attack patterns align with those documented in the MITRE ATT&CK framework under techniques related to privilege escalation and information gathering.
The mitigation strategy for CVE-2018-6920 primarily involves upgrading to the patched versions of FreeBSD that contain proper memory initialization routines in both the Linux subsystem and Atheros wireless driver components. System administrators should prioritize updating their FreeBSD installations to versions 11.1-STABLE(r332303), 11.1-RELEASE-p10, 10.4-STABLE(r332321), or 10.4-RELEASE-p9, which include the necessary patches to address the insufficient memory initialization. Additionally, organizations should implement monitoring for unauthorized local access attempts and consider implementing additional security controls such as mandatory access controls or enhanced logging mechanisms to detect potential exploitation attempts. The vulnerability highlights the importance of proper memory management practices in kernel code and demonstrates how seemingly minor implementation flaws can create significant security implications in operating system security models.