CVE-2023-6660 in FreeBSD
Summary
by MITRE • 12/13/2023
When a program running on an affected system appends data to a file via an NFS client mount, the bug can cause the NFS client to fail to copy in the data to be written but proceed as though the copy operation had succeeded. This means that the data to be written is instead replaced with whatever data had been in the packet buffer previously. Thus, an unprivileged user with access to an affected system may abuse the bug to trigger disclosure of sensitive information. In particular, the leak is limited to data previously stored in mbufs, which are used for network transmission and reception, and for certain types of inter-process communication. The bug can also be triggered unintentionally by system applications, in which case the data written by the application to an NFS mount may be corrupted. Corrupted data is written over the network to the NFS server, and thus also susceptible to being snooped by other hosts on the network. Note that the bug exists only in the NFS client; the version and implementation of the server has no effect on whether a given system is affected by the problem.
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Analysis
by VulDB Data Team • 01/07/2024
The vulnerability described in CVE-2023-6660 represents a critical flaw in the Network File System (NFS) client implementation that manifests when data is appended to files through NFS mounts. This issue falls under the category of data corruption and information disclosure vulnerabilities, specifically categorized as CWE-129 Input Validation and CWE-200 Information Exposure. The vulnerability exists exclusively within the NFS client component and does not affect the NFS server implementation, making it particularly challenging to identify and mitigate since the problem originates from client-side operations that appear to succeed but actually fail silently.
The technical mechanism behind this vulnerability involves a failure in the data copy operation within the NFS client's file append functionality. When a program attempts to append data to a file through an NFS mount, the client incorrectly reports successful completion of the write operation while simultaneously failing to properly copy the intended data. Instead, the system writes data that was previously stored in network packet buffers, commonly known as mbufs, which are essential components for network transmission and reception as well as inter-process communication. This behavior creates a scenario where sensitive information previously handled by the network stack becomes inadvertently exposed through the file system operations.
The operational impact of this vulnerability extends beyond simple data corruption to encompass serious security implications. An unprivileged user with access to an affected system can exploit this bug to disclose sensitive information that was previously stored in mbufs, potentially exposing confidential data from other network operations or processes. The vulnerability is particularly concerning because it can be triggered unintentionally by system applications, meaning that legitimate operations may become corrupted without explicit user intervention. This silent failure mode makes the vulnerability difficult to detect and debug, as the system continues to operate seemingly normally while silently corrupting data.
The data corruption affects network transmission to NFS servers, creating a potential attack surface where data written to NFS mounts becomes corrupted and subsequently transmitted over the network. This creates opportunities for network sniffing attacks where other hosts on the same network segment can intercept and read the corrupted data, which may contain sensitive information from other processes or previous network communications. The vulnerability's impact is amplified by its ability to affect both user-level applications and system-level processes, potentially compromising the integrity of critical system operations that depend on NFS for file storage and access. Organizations implementing NFS services should consider this vulnerability as a potential vector for data leakage and integrity compromise, particularly in environments where network monitoring is present and where sensitive data flows through NFS mounts. The issue aligns with ATT&CK techniques related to data manipulation and information disclosure, specifically targeting the integrity of network-based file operations.
Mitigation strategies should focus on immediate patching of affected NFS client implementations, along with network segmentation and monitoring to detect anomalous data transmission patterns. System administrators should implement network intrusion detection systems to monitor for unusual data flows that might indicate corrupted data being transmitted through NFS mounts. Additionally, organizations should consider implementing access controls and privilege restrictions on NFS mount points to limit potential exploitation opportunities, while also conducting thorough audits of NFS usage patterns to identify any abnormal file operations that might indicate corruption. The vulnerability demonstrates the importance of thorough testing of network stack components and the potential for seemingly benign operations to create significant security risks in distributed computing environments.