CVE-2005-3531 in fuse
Summary
by MITRE
fusermount in fuse before 2.4.1 if installed setuid root allows local users to corrupt /etc/mtab and possibly modify mount options by performing a mount over a directory whose name contains certain special characters.
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Analysis
by VulDB Data Team • 06/12/2019
The vulnerability identified as CVE-2005-3531 affects the fusermount utility within the Filesystem in Userspace (FUSE) framework prior to version 2.4.1. This issue represents a significant security flaw that arises from improper privilege handling and input validation within the setuid root execution context. The vulnerability specifically targets the mount management functionality where fusermount operates with elevated privileges to manage filesystem mounts, creating a potential attack surface for local privilege escalation and system integrity compromise.
The technical flaw stems from the improper handling of directory names containing special characters during mount operations. When fusermount processes mount requests, it fails to adequately sanitize or validate the mount point names, particularly those containing characters that could be interpreted as special shell metacharacters or path manipulation indicators. This weakness allows attackers to craft malicious mount point names that can manipulate the /etc/mtab file through the setuid execution context. The vulnerability is particularly dangerous because it leverages the privileged execution environment of fusermount to modify system configuration files that track mounted filesystems.
The operational impact of this vulnerability extends beyond simple file corruption as it provides attackers with the ability to manipulate mount options and potentially gain unauthorized access to system resources. By exploiting the special character handling flaw, local users can corrupt the /etc/mtab file which serves as a critical system file tracking all currently mounted filesystems. This corruption can lead to system instability, incorrect mount point reporting, and potentially enable attackers to modify mount options in ways that could grant them additional privileges or access to restricted filesystem areas. The vulnerability is classified under CWE-20 as "Improper Input Validation" and specifically relates to CWE-78 as "Improper Neutralization of Special Elements used in an OS Command" due to the shell metacharacter handling issues.
The security implications of this vulnerability align with ATT&CK techniques including T1068 "Exploitation for Privilege Escalation" and T1548.001 "Abuse Elevation Control Mechanism". Attackers can leverage this flaw to escalate privileges from local user to root level by manipulating the mount point handling process. The exploitation requires local system access but can result in significant system compromise, making it particularly dangerous in multi-user environments or when combined with other local privilege escalation vectors. The vulnerability demonstrates a classic example of how setuid binaries can create dangerous attack surfaces when proper input validation and sanitization are not implemented.
Mitigation strategies for CVE-2005-3531 involve immediate patching of the FUSE framework to version 2.4.1 or later, which includes proper input validation and sanitization of mount point names. System administrators should also implement monitoring for unauthorized modifications to the /etc/mtab file and consider implementing additional security controls such as file integrity monitoring solutions. The vulnerability highlights the importance of proper privilege separation and input validation in setuid applications, emphasizing that all user-supplied input must be rigorously validated before processing in privileged contexts. Organizations should also review their FUSE implementations and ensure that all related utilities properly handle special characters and maintain appropriate security boundaries between privileged and unprivileged execution contexts.