CVE-1999-0166 in NFS
Summary
by MITRE
nfs allows users to use a "cd .." command to access other directories besides the exported file system.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability described in CVE-1999-0166 represents a critical directory traversal flaw within the Network File System implementation that allows unauthorized access to filesystem resources beyond the intended exported directories. This issue specifically affects the nfs daemon implementation where the "cd .." command functionality enables users to navigate to parent directories that should be restricted, effectively bypassing the security boundaries that normally protect exported filesystems from arbitrary access. The flaw stems from improper handling of directory navigation commands within the nfs protocol implementation, where the system fails to properly validate or restrict path traversal operations that could lead to privilege escalation and unauthorized data access.
The technical implementation of this vulnerability demonstrates a classic path traversal weakness that can be exploited through the nfs client-server communication model. When users execute the "cd .." command against an nfs exported filesystem, the nfs daemon does not properly enforce the boundaries of the exported directory tree, allowing attackers to navigate upward through the filesystem hierarchy and potentially access sensitive directories and files that should remain isolated from client access. This behavior violates fundamental security principles of filesystem isolation and privilege separation that are essential for maintaining secure network file sharing environments. The vulnerability operates at the protocol level where the nfs implementation fails to properly sanitize or validate directory navigation requests, creating an attack vector that can be exploited by both local and remote users.
The operational impact of this vulnerability extends beyond simple unauthorized file access, as it can enable attackers to discover and potentially access sensitive system files, configuration data, and other restricted resources that may contain credentials, system information, or other valuable assets. This weakness can be particularly dangerous in enterprise environments where nfs is commonly used for shared storage solutions, as it allows attackers to bypass the intended security boundaries and gain access to data that should remain protected within the exported filesystem. The vulnerability also potentially enables further exploitation techniques including privilege escalation, information disclosure, and denial of service attacks that can compromise the integrity and availability of the entire nfs infrastructure.
Mitigation strategies for this vulnerability should focus on implementing proper path validation and boundary enforcement within the nfs daemon implementation, ensuring that directory traversal commands are properly sanitized and restricted to the intended exported filesystem boundaries. System administrators should implement proper network segmentation and access controls to limit nfs service exposure, while also applying the latest security patches and updates from vendors. The implementation should include strict enforcement of directory access controls and path validation mechanisms that prevent upward directory traversal operations from escaping the designated export points. Organizations should also consider implementing monitoring and logging of nfs access patterns to detect and respond to potential exploitation attempts. This vulnerability aligns with CWE-22 Directory Traversal and can be mapped to ATT&CK technique T1071.004 Application Layer Protocol: DNS to understand how network protocols can be abused for privilege escalation and information gathering activities. The remediation process should include comprehensive testing of nfs implementations to ensure that path traversal protections are properly enforced and that all exported filesystems maintain their intended security boundaries.