CVE-2010-2020 in FreeBSD
Summary
by MITRE
sys/nfsclient/nfs_vfsops.c in the NFS client in the kernel in FreeBSD 7.2 through 8.1-PRERELEASE, when vfs.usermount is enabled, does not validate the length of a certain fhsize parameter, which allows local users to gain privileges via a crafted mount request.
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Analysis
by VulDB Data Team • 01/25/2025
The vulnerability described in CVE-2010-2020 resides within the Network File System (NFS) client implementation in FreeBSD operating systems version 7.2 through 8.1-PRERELEASE. This issue specifically affects the kernel-level component responsible for managing NFS filesystem operations, particularly in the sys/nfsclient/nfs_vfsops.c file. The vulnerability emerges when the vfs.usermount parameter is enabled, which allows non-root users to mount filesystems, creating a potential attack surface that malicious users can exploit to escalate their privileges within the system.
The technical flaw manifests in the improper validation of the fhsize parameter during mount requests. The fhsize parameter represents the size of the file handle used by NFS to identify files and directories across the network. When this parameter is not properly validated, an attacker can craft a malicious mount request that supplies an oversized or malformed fhsize value. This lack of input validation creates a buffer overread condition that can be leveraged to manipulate kernel memory structures and potentially execute arbitrary code with elevated privileges.
The operational impact of this vulnerability is significant as it transforms a local privilege escalation opportunity into a critical security risk. Attackers who can execute code on a FreeBSD system with vfs.usermount enabled can exploit this flaw to gain root privileges, effectively compromising the entire system. This vulnerability directly relates to CWE-129, which addresses improper validation of input buffers, and CWE-787, which covers out-of-bounds write conditions. The attack vector requires local access and the ability to perform mount operations, but the privilege escalation aspect makes it particularly dangerous for systems where users might have limited administrative access but can still mount filesystems.
From an adversarial perspective, this vulnerability aligns with ATT&CK techniques focusing on privilege escalation and local execution. The attack follows a pattern where adversaries leverage kernel-level flaws to bypass system security controls and achieve elevated privileges. The vulnerability demonstrates how seemingly benign user mount capabilities can become dangerous when combined with improper kernel input validation. Organizations running affected FreeBSD versions should immediately apply patches and consider disabling vfs.usermount if the functionality is not required. The mitigation strategy involves both immediate patch deployment and operational security measures such as monitoring for unauthorized mount operations and implementing least privilege principles for user access to filesystem mounting capabilities.
This vulnerability represents a classic example of how kernel-level buffer overread conditions can be exploited for privilege escalation, highlighting the critical importance of proper input validation in kernel space operations. The flaw underscores the necessity of robust security testing for kernel components and the potential consequences when such validation is omitted or insufficiently implemented in security-critical system functions.