CVE-2010-3879 in FUSE
Summary
by MITRE
FUSE, possibly 2.8.5 and earlier, allows local users to create mtab entries with arbitrary pathnames, and consequently unmount any filesystem, via a symlink attack on the parent directory of the mountpoint of a FUSE filesystem, a different vulnerability than CVE-2010-0789.
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Analysis
by VulDB Data Team • 10/07/2024
The vulnerability described in CVE-2010-3879 affects the Filesystem in Userspace (FUSE) framework, specifically versions 2.8.5 and earlier, presenting a significant local privilege escalation and system integrity compromise risk. This issue arises from improper handling of symbolic link attacks during the mounting process, allowing malicious local users to manipulate the /etc/mtab file through carefully crafted symlink manipulation. The flaw enables attackers to create arbitrary pathnames within the mount table entries, ultimately granting them the ability to unmount any filesystem regardless of permissions or security boundaries. This vulnerability operates by exploiting the lack of proper symlink resolution checks when creating mount entries, making it particularly dangerous in multi-user environments where local users might not have direct access to system mount operations. The vulnerability is distinct from CVE-2010-0789, indicating a separate attack vector within the same software ecosystem that requires different mitigation approaches.
The technical implementation of this vulnerability exploits the race condition and symlink traversal mechanisms inherent in FUSE's mountpoint handling. When a FUSE filesystem is mounted, the system creates entries in the /etc/mtab file that reference the actual mountpoint location. However, due to insufficient validation of symbolic links in the parent directory path, an attacker can create a malicious symlink that points to a location where they can write to the mtab file. This allows them to inject arbitrary entries into the mount table that reference filesystems they do not normally have access to unmount. The flaw stems from the improper use of path resolution functions that do not adequately verify the integrity of symbolic links in the parent directory hierarchy, creating a path traversal attack surface that can be exploited by local users. This behavior aligns with CWE-367 weakness classification, which addresses Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities where the state of a resource changes between the time it is checked and when it is used.
The operational impact of CVE-2010-3879 extends beyond simple local privilege escalation to encompass potential system instability and data integrity compromise. Attackers can leverage this vulnerability to unmount critical filesystems, potentially causing system crashes, data loss, or service interruptions. The ability to manipulate the mtab file also allows for persistent modifications that could be used to hide mounted filesystems from normal system monitoring tools, making detection more difficult. In enterprise environments, this vulnerability could enable attackers to disrupt services, gain access to sensitive data through mounted filesystems, or create backdoor access points by manipulating mount points. The vulnerability affects system stability because it allows unmounting of filesystems that should remain mounted for system operation, potentially causing cascading failures in dependent services or applications that rely on specific mount points. Network security monitoring tools may not detect this attack vector because it operates at the local filesystem level and does not involve network traffic or external connections.
Mitigation strategies for CVE-2010-3879 should focus on both immediate patching and operational security improvements. The primary solution involves upgrading to FUSE versions that address this vulnerability, typically those newer than 2.8.5, where proper symlink validation has been implemented. Organizations should also implement mandatory access controls and file system permissions that limit the ability of local users to manipulate mount points and mtab entries. System administrators should regularly audit mount point configurations and monitor for unauthorized changes to critical system files like /etc/mtab. Additionally, implementing proper file system hardening measures such as read-only mount points for sensitive configuration files, using SELinux or AppArmor policies to restrict FUSE operations, and employing intrusion detection systems that monitor for suspicious mount table modifications can significantly reduce the risk. The vulnerability demonstrates the importance of proper input validation and path resolution in system-level operations, aligning with ATT&CK technique T1068 which covers local privilege escalation through improper privilege handling. Regular security assessments and vulnerability scanning should include checks for outdated FUSE installations and proper implementation of file system access controls to prevent exploitation of similar TOCTOU vulnerabilities.