CVE-2011-0542 in fuse
Summary
by MITRE
fusermount in fuse 2.8.5 and earlier does not perform a chdir to / before performing a mount or umount, which allows local users to unmount arbitrary directories via unspecified vectors.
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Analysis
by VulDB Data Team • 11/18/2021
The vulnerability identified as CVE-2011-0542 affects the fuse (Filesystem in Userspace) package version 2.8.5 and earlier, specifically within the fusermount utility. This flaw represents a significant security oversight that stems from improper privilege management during filesystem operations. The core issue lies in the fusermount utility's failure to change the current working directory to the root directory before executing mount or unmount operations, creating a path traversal vulnerability that local attackers can exploit to manipulate filesystem mounts.
The technical implementation of this vulnerability involves the fusermount utility operating with elevated privileges during mount and unmount operations but without proper directory context management. When a user executes fusermount commands, the utility does not perform a chdir to / before carrying out filesystem operations, allowing attackers to manipulate the current working directory to point to arbitrary locations. This behavior creates opportunities for privilege escalation and unauthorized filesystem manipulation through unspecified attack vectors that leverage the utility's elevated permissions.
From an operational perspective, this vulnerability enables local users to unmount arbitrary directories that they might not normally have access to, potentially compromising system integrity and data availability. The impact extends beyond simple filesystem manipulation as attackers can exploit this to disrupt services, hide malicious activities, or gain deeper system access by manipulating mounted filesystems. The vulnerability particularly affects systems where fuse is used for user-space filesystem implementations, making it relevant to a broad range of Unix-like operating systems including various linux distributions and other unix-based platforms.
The security implications of this vulnerability align with CWE-22 Path Traversal and CWE-787 Out-of-bounds Write patterns, as the flaw involves improper handling of directory paths during privileged operations. This vulnerability also maps to ATT&CK technique T1068, Privilege Escalation, and T1485, Data Destruction, as local attackers can leverage the elevated privileges to perform unauthorized operations on mounted filesystems. The exploitability of this vulnerability is enhanced by the fact that fusermount typically runs with root privileges, making it a prime target for local privilege escalation attacks.
Mitigation strategies for CVE-2011-0542 include updating to fuse version 2.8.6 or later, where the chdir functionality has been properly implemented. System administrators should also review and restrict access to the fusermount utility, ensuring that only trusted users can execute it with elevated privileges. Additional protective measures include implementing proper directory context management in custom applications that utilize fuse functionality, and conducting regular security audits to identify similar privilege escalation vulnerabilities in other system utilities. The fix addresses the root cause by ensuring that all mount and unmount operations occur from a known safe directory context, eliminating the path traversal vectors that made this vulnerability exploitable.