CVE-2005-2876 in util-linux
Summary
by MITRE
umount in util-linux 2.8 to 2.12q 2.13-pre1 and 2.13-pre2 and other packages such as loop-aes-utils allows local users with unmount permissions to gain privileges via the -r (remount) option which causes the file system to be remounted with just the read-only flag which effectively clears the nosuid nodev and other flags.
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Analysis
by VulDB Data Team • 06/09/2019
This vulnerability exists in the umount command functionality within util-linux versions ranging from 2.8 through 2.12q and including 2.13-pre1 and 2.13-pre2, as well as in related packages like loop-aes-utils. The flaw specifically manifests when local users possess unmount permissions but attempt to utilize the -r (remount) option during the unmount process. The technical mechanism involves the umount command incorrectly handling the remount operation by applying only the read-only flag while simultaneously clearing critical mount flags such as nosuid and nodev. This behavior creates a privilege escalation vector because the removal of these security flags effectively weakens the filesystem protection mechanisms that prevent unauthorized code execution and device access. The vulnerability represents a classic case of improper privilege handling and flag management in system utilities that directly impact the security posture of Unix-like operating systems.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system security implications. When the nosuid flag is cleared, it allows setuid binaries to execute with elevated privileges, while the removal of nodev disables protections against device file access that could otherwise prevent exploitation of device drivers or hardware interfaces. Attackers can leverage this to gain unauthorized access to system resources and potentially escalate privileges to root level. The vulnerability is particularly concerning because it requires minimal privileges to exploit and can be triggered through normal system operations that involve unmounting filesystems. This makes it a persistent threat in environments where users have legitimate unmount permissions but should not be granted additional privileges through filesystem manipulation.
The vulnerability maps directly to CWE-276, which addresses improper privileges, and aligns with ATT&CK techniques related to privilege escalation and persistence. Specifically, it enables the T1068 privilege escalation technique by allowing local users to manipulate mount flags to bypass security controls. The attack vector is particularly relevant in multi-user environments where users may have legitimate need to unmount filesystems but should not be able to modify mount options that affect system security. Security researchers have identified this as a critical issue in system utilities that handle mount operations, as it demonstrates how seemingly benign filesystem management commands can be exploited to undermine fundamental security mechanisms. Organizations should consider implementing access controls and monitoring for unauthorized mount and unmount operations, particularly when the -r flag is used in conjunction with filesystem management tasks. The vulnerability underscores the importance of maintaining proper security boundaries in system utilities and validating all mount option combinations to prevent unintended privilege escalation scenarios that could compromise entire system environments.
This issue highlights the critical importance of proper input validation and privilege management in system utilities. The vulnerability demonstrates how mount flag handling in filesystem management tools can create security weaknesses that attackers can exploit to bypass fundamental security controls. The flaw exists because the system does not properly validate or restrict the combination of mount options that users can apply during unmount operations, creating an unintended pathway for privilege escalation. Security professionals should implement comprehensive monitoring of filesystem operations and ensure that system utilities properly enforce security policies during mount and unmount operations. The vulnerability also emphasizes the need for regular security assessments of core system utilities and the importance of maintaining up-to-date system software to prevent exploitation of known weaknesses in filesystem management tools.