CVE-2001-1017 in FreeBSD
Summary
by MITRE
rmuser utility in FreeBSD 4.2 and 4.3 creates a copy of the master.passwd file with world-readable permissions while updating the original file, which could allow local users to gain privileges by reading the copied file while rmuser is running, obtain the password hashes, and crack the passwords.
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Analysis
by VulDB Data Team • 02/11/2017
The vulnerability identified as CVE-2001-1017 represents a critical privilege escalation flaw in the FreeBSD operating system versions 4.2 and 4.3. This issue resides within the rmuser utility which is responsible for removing user accounts from the system. The flaw demonstrates a classic security misconfiguration where temporary file handling creates an exploitable window of opportunity for local attackers. The root cause stems from improper file permission management during the user deletion process, creating a race condition that adversaries can leverage for unauthorized access.
The technical implementation of this vulnerability occurs when the rmuser utility executes its operations. During the account removal process, the utility creates a temporary copy of the master.passwd file while simultaneously updating the original file. This temporary copy is created with world-readable permissions, meaning any local user on the system can access this file. The timing of this operation creates a critical window where the copied file contains sensitive authentication data including password hashes that remain accessible to all users. This design flaw directly violates the principle of least privilege and demonstrates poor security hygiene in temporary file management.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass full credential compromise. Attackers exploiting this flaw can obtain password hashes from the temporary file, which they can then attempt to crack using various password recovery techniques. The vulnerability affects the entire local user base since any user can access the world-readable temporary file. This creates a significant risk for systems where multiple users share the same machine, particularly in multi-user environments such as development servers, shared workstations, or networked systems where local privilege escalation can lead to broader system compromise.
The security implications of this vulnerability align with CWE-732, which addresses incorrect permissions for critical resources, and relates to ATT&CK technique T1068 which covers local privilege escalation through system binary manipulation. The flaw represents a fundamental failure in secure file handling practices where temporary files are not properly secured during system operations. Organizations running affected FreeBSD versions face potential unauthorized access to user accounts, credential theft, and possible lateral movement within their network infrastructure. This vulnerability underscores the importance of proper file permission management and the need for secure temporary file creation practices in system utilities.
Mitigation strategies for this vulnerability require immediate system updates to patched FreeBSD versions that address the improper file permission handling in the rmuser utility. System administrators should also implement monitoring for unauthorized access to system files and consider implementing additional security controls such as file integrity monitoring solutions. The recommended approach includes ensuring that temporary files created during system operations are created with restrictive permissions and are automatically cleaned up after use. Additionally, organizations should conduct regular security audits of system utilities to identify similar permission-related vulnerabilities and implement proper access controls to prevent unauthorized file access during critical system operations.