CVE-2007-0004 in Red Hat
Summary
by MITRE
The NFS client implementation in the kernel in Red Hat Enterprise Linux (RHEL) 3, when a filesystem is mounted with the noacl option, checks permissions for the open system call via vfs_permission (mode bits) data rather than an NFS ACCESS call to the server, which allows local client processes to obtain a false success status from open calls that the server would deny, and possibly obtain sensitive information about file permissions on the server, as demonstrated in a root_squash environment. NOTE: it is uncertain whether any scenarios involving this issue cross privilege boundaries.
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Analysis
by VulDB Data Team • 11/02/2017
The vulnerability described in CVE-2007-0004 represents a critical access control flaw within the Network File System (NFS) client implementation of Red Hat Enterprise Linux version 3. This issue manifests when an NFS filesystem is mounted with the noacl option, which fundamentally alters how permission checks are performed during file operations. The core technical flaw lies in the kernel's handling of open system calls where it relies on local virtual file system permission checks rather than authenticating with the NFS server through proper ACCESS calls. This design decision creates a significant security gap that undermines the integrity of the NFS security model.
The operational impact of this vulnerability is substantial as it enables local client processes to obtain false positive results from open calls that the server would legitimately deny. This occurs because the client-side permission checking bypasses the server's actual access control mechanisms, allowing unauthorized access to files that should be restricted. In environments utilizing root_squash, where the server maps root user privileges to an unprivileged user ID, the vulnerability becomes particularly dangerous as local processes can potentially gain insights into file permission structures that would otherwise remain hidden from them. The security implications extend beyond simple access violations to include information disclosure risks that could expose sensitive server-side permission configurations.
This vulnerability directly relates to CWE-284, which addresses improper access control in software implementations, and demonstrates how improper privilege management can create security holes in distributed file systems. The issue also aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' through the exploitation of system-level vulnerabilities. The flaw essentially creates a path for local privilege escalation or information gathering that bypasses the intended security boundaries of the NFS protocol. The uncertainty regarding whether this issue crosses privilege boundaries reflects the complex nature of distributed security models where local client behavior can influence server-side access controls.
Mitigation strategies for this vulnerability include avoiding the use of the noacl mount option when mounting NFS filesystems, particularly in security-sensitive environments. System administrators should implement proper NFS server configurations that do not rely on client-side permission checking for critical security functions. The recommended approach involves ensuring that NFS mounts perform proper ACCESS calls to the server rather than relying on local permission checks. Additionally, organizations should consider upgrading to newer versions of RHEL that have addressed this specific kernel implementation flaw, as the vulnerability represents an outdated security model that has been corrected in subsequent releases. Regular security audits of NFS configurations should include verification that appropriate mount options are used and that access control mechanisms function as intended.