CVE-2020-7455 in FreeBSD
Summary
by MITRE
In FreeBSD 12.1-STABLE before r360973, 12.1-RELEASE before p5, 11.4-STABLE before r360973, 11.4-BETA1 before p1 and 11.3-RELEASE before p9, the FTP packet handler in libalias incorrectly calculates some packet length allowing disclosure of small amounts of kernel (for kernel NAT) or natd process space (for userspace natd).
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Analysis
by VulDB Data Team • 10/18/2020
The vulnerability identified as CVE-2020-7455 represents a critical information disclosure flaw within the FreeBSD operating system's network packet handling mechanisms. This issue specifically affects the libalias library which serves as the core component responsible for network address translation operations in FreeBSD systems. The flaw exists in multiple FreeBSD release versions including 12.1-STABLE, 11.4-STABLE, and various beta and release versions of FreeBSD 11.3 and 11.4, making it a widespread concern across several system generations. The vulnerability manifests in the FTP packet handler implementation where incorrect packet length calculations occur during network address translation processes.
The technical root cause of this vulnerability lies in improper packet length validation within the libalias library's FTP handling code. When the system processes FTP packets for NAT operations, either in kernel mode or userspace natd processes, the packet length calculations fail to properly account for all data segments. This miscalculation creates a condition where adjacent memory regions become accessible through crafted network packets, allowing attackers to read small portions of kernel memory space or natd process memory. The vulnerability specifically impacts the NAT functionality that FreeBSD employs to translate private IP addresses to public addresses for internet communication, particularly affecting FTP traffic which requires complex data channel handling.
The operational impact of CVE-2020-7455 extends beyond simple information disclosure, as it provides attackers with potential access to sensitive kernel memory structures that could reveal system configuration details, memory layout information, or other confidential data. This type of memory disclosure vulnerability can serve as a stepping stone for more sophisticated attacks, potentially enabling attackers to gather intelligence about the target system's memory organization, which could be leveraged in subsequent exploitation attempts. The vulnerability affects both kernel-based NAT operations and userspace natd processes, meaning that systems utilizing either approach for network address translation are at risk. The small amount of memory disclosed per packet makes this vulnerability particularly insidious as it may not immediately trigger detection mechanisms, yet can accumulate sufficient information over time to aid in further attacks.
From a cybersecurity perspective, this vulnerability aligns with CWE-200, which describes "Information Exposure" and represents a classic case of memory disclosure through improper input validation. The issue demonstrates characteristics consistent with ATT&CK technique T1082, where adversaries gather system information through reconnaissance activities that can reveal memory structures and system configurations. Organizations running FreeBSD systems with NAT functionality should prioritize immediate patching to address this vulnerability, as the affected versions include multiple stable and release branches that remain in active use. The patching process requires updating to the specific FreeBSD releases that contain the corrected libalias implementation, with particular attention to versions following r360973 for the stable branches and the corresponding release patches for p5, p1, and p9 versions. System administrators should also consider monitoring network traffic for unusual FTP patterns that might indicate exploitation attempts, while ensuring proper network segmentation to limit the potential impact of any successful exploitation attempts.