CVE-2001-0120 in shadow-utils
Summary
by MITRE
useradd program in shadow-utils program may allow local users to overwrite arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 05/01/2019
The vulnerability identified as CVE-2001-0120 resides within the useradd program of the shadow-utils package, a critical component in Unix-like operating systems responsible for user account management. This flaw represents a classic symlink attack vector that exploits the insecure handling of temporary files during user creation processes. The vulnerability specifically affects systems where the useradd utility creates temporary files without proper security checks, allowing local attackers to manipulate symbolic links and potentially overwrite arbitrary files with elevated privileges.
The technical implementation of this vulnerability stems from the useradd program's failure to validate file paths properly when creating temporary files during user account creation. When the program executes, it may create temporary files in predictable locations without ensuring proper file permissions or verifying that symbolic links are not present in the path. An attacker can exploit this by creating malicious symbolic links in the expected temporary file locations before executing the useradd command, causing the program to write data to locations controlled by the attacker rather than the intended target. This behavior directly maps to CWE-377, which addresses insecure temporary file handling, and CWE-378, which covers the creation of temporary files with insecure permissions.
The operational impact of this vulnerability extends beyond simple file overwriting, as it provides a pathway for privilege escalation attacks that can compromise system integrity. Local users who can execute the useradd command or who have access to systems where this utility runs with elevated privileges can leverage this vulnerability to overwrite critical system files, configuration files, or even binary executables. The attack vector is particularly concerning because it operates at the system level where the useradd utility typically runs with root privileges, making it a significant escalation point for attackers seeking persistent access. This vulnerability aligns with ATT&CK technique T1068, which covers local privilege escalation through exploitation of system vulnerabilities, and T1059, which encompasses the execution of commands through system utilities.
Mitigation strategies for CVE-2001-0120 require immediate system hardening and patching of affected shadow-utils versions. Organizations should ensure that all systems running the useradd utility have been updated to patched versions that properly handle temporary file creation with secure permissions and path validation. System administrators should implement proper file system permissions and access controls, particularly around temporary directories and user account management utilities. Additional protective measures include monitoring for unauthorized execution of useradd commands, implementing file integrity monitoring solutions, and conducting regular security audits of system utilities to identify similar insecure file handling patterns. The vulnerability also underscores the importance of following secure coding practices such as using secure temporary file creation methods, validating all file paths, and ensuring proper privilege separation in system utilities. Organizations should consider implementing privilege escalation controls and monitoring mechanisms that can detect anomalous file modification patterns that might indicate exploitation attempts.