CVE-2011-1676 in Linux
Summary
by MITRE
mount in util-linux 2.19 and earlier does not remove the /etc/mtab.tmp file after a failed attempt to add a mount entry, which allows local users to trigger corruption of the /etc/mtab file via multiple invocations.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability identified as CVE-2011-1676 resides within the mount utility of util-linux version 2.19 and earlier, representing a significant flaw in system file management that can lead to persistent corruption of critical system files. This issue specifically affects the /etc/mtab file which serves as a crucial component in Unix-like operating systems for tracking currently mounted filesystems and their properties. The mount utility is responsible for managing filesystem mounts and maintaining this essential file that documents all active mount points within the system.
The technical flaw manifests when the mount command encounters a failure during the process of adding a new mount entry to the /etc/mtab file. Under normal circumstances, the mount utility creates a temporary file named /etc/mtab.tmp during the update process, which should be properly removed upon successful completion or failure of the operation. However, in vulnerable versions, when a mount operation fails, the utility neglects to remove this temporary file, leaving it in place on the filesystem. This oversight becomes particularly problematic when multiple mount operations are performed sequentially, as each failed attempt leaves behind a stale temporary file that can interfere with subsequent operations.
The operational impact of this vulnerability extends beyond simple file corruption, as it creates a persistent state where the /etc/mtab file can become increasingly malformed with each failed mount attempt. Local users can exploit this weakness by repeatedly invoking mount commands that are designed to fail, thereby accumulating multiple temporary files that interfere with the proper functioning of the mount system. This leads to corruption of the mount table, potentially causing system instability, incorrect mount point reporting, and in severe cases, preventing legitimate mount operations from succeeding properly. The vulnerability essentially creates a denial-of-service condition that affects the core filesystem management functionality of the operating system.
This flaw aligns with CWE-116, which addresses improper encoding or handling of special characters, and more specifically relates to CWE-362, which covers concurrent execution using shared resource with improper synchronization. The vulnerability also maps to ATT&CK technique T1059, which involves the use of command and scripting interpreters, as attackers could leverage this weakness through repeated command execution to cause system instability. Additionally, the issue connects to T1490, which deals with data destruction, as the corruption of the /etc/mtab file represents a form of data integrity compromise that can affect system stability and security posture. The vulnerability demonstrates a classic example of improper resource cleanup and temporary file management, where the failure to properly handle temporary files during error conditions creates a persistent security risk that can be exploited by local users to degrade system functionality and potentially gain unauthorized access to system resources through manipulation of critical filesystem information.
Mitigation strategies for this vulnerability require immediate patching of affected systems to upgrade to util-linux versions that properly handle temporary file cleanup during mount operations. System administrators should implement monitoring procedures to detect the presence of stale /etc/mtab.tmp files and establish automated cleanup processes to remove these temporary files. Additionally, implementing proper file system permissions and access controls can limit the ability of local users to repeatedly invoke mount operations that could lead to exploitation. Regular system audits should verify the integrity of the /etc/mtab file and ensure that no stale temporary files persist on the system. Organizations should also consider implementing intrusion detection systems that can identify unusual patterns of mount command usage that might indicate attempted exploitation of this vulnerability. The most effective long-term solution involves ensuring all systems maintain up-to-date util-linux packages that have been patched to properly handle temporary file cleanup in error conditions, thereby preventing the accumulation of stale temporary files that could lead to mount table corruption and system instability.