CVE-2014-1638 in localepurge
Summary
by MITRE
(1) debian/postrm and (2) debian/localepurge.config in localepurge before 0.7.3.2 use tempfile to create a safe temporary file but appends a suffix to the original filename and writes to this new filename, which allows local users to overwrite arbitrary files via a symlink attack on the new filename.
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Analysis
by VulDB Data Team • 03/06/2019
The vulnerability identified as CVE-2014-1638 resides within the localepurge package version 0.7.3.1 and earlier, specifically affecting the debian/postrm and debian/localepurge.config scripts. This issue represents a classic symlink attack scenario that exploits improper temporary file handling mechanisms. The vulnerability manifests when the package's post-removal script attempts to create a temporary file using the tempfile utility but subsequently appends a suffix to the original filename before writing to the new filename. This seemingly innocuous approach creates a dangerous race condition that malicious local users can exploit to overwrite arbitrary files on the system.
The technical flaw stems from a fundamental misunderstanding of how temporary file creation should be handled in Unix-like systems. When the localepurge package creates a temporary file, it follows a pattern that generates a new filename with a suffix appended to the original name. However, this approach fails to account for the possibility that an attacker could establish a symbolic link with the new filename before the legitimate process attempts to write to it. This creates a window where the attacker's symlink can be exploited to redirect file operations to arbitrary locations, effectively allowing privilege escalation and file manipulation attacks. The vulnerability directly maps to CWE-367, which describes the Time-of-Check to Time-of-Use (TOCTOU) race condition, where the system state changes between the time it is checked and when it is used. This weakness enables attackers to manipulate file operations through carefully crafted symbolic links that exploit the temporary file creation process.
The operational impact of this vulnerability is significant for systems running affected versions of localepurge, as it allows local users to perform unauthorized file overwrites with potentially elevated privileges. The attack vector requires local system access but does not need network connectivity or external exploitation. An attacker could leverage this vulnerability to overwrite critical system files, configuration files, or even executable programs, potentially leading to privilege escalation or persistent backdoors. The vulnerability affects systems where localepurge is used to manage locale-related files and can be particularly dangerous in multi-user environments where local privilege escalation could lead to broader system compromise. This issue particularly impacts Debian-based systems and other distributions that utilize the localepurge package for locale management and cleanup operations.
The recommended mitigations for CVE-2014-1638 involve immediate upgrading to localepurge version 0.7.3.2 or later, which contains the necessary fixes to properly handle temporary file creation without exposing the system to symlink attacks. System administrators should also implement proper file permissions and access controls to limit the impact of potential exploitation attempts. Additionally, monitoring for unauthorized file modifications and implementing proper logging of system package operations can help detect exploitation attempts. The fix implemented in version 0.7.3.2 likely involves using more secure temporary file creation methods that ensure atomicity and prevent the race condition that enables the symlink attack. Organizations should also consider implementing the principle of least privilege for system users and regularly auditing package installations and removals to prevent exploitation of similar vulnerabilities. This vulnerability demonstrates the importance of proper temporary file handling practices and the need for security reviews of system administration scripts that interact with file systems.