CVE-2000-1135 in Linux
Summary
by MITRE
fshd (fsh daemon) in Debian GNU/Linux allows local users to overwrite files of other users via a symlink attack.
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Analysis
by VulDB Data Team • 05/28/2018
The fshd daemon vulnerability represents a critical local privilege escalation issue within Debian GNU/Linux systems that has significant implications for system security and data integrity. This vulnerability specifically affects the fsh daemon which is responsible for handling file system operations and user interactions within the Debian environment. The flaw manifests through a symlink attack vector that allows local users to manipulate file permissions and overwrite files belonging to other users, creating a serious breach in system isolation and user privilege management.
The technical implementation of this vulnerability stems from improper handling of symbolic links within the fshd daemon's file operations. When the daemon processes file system requests, it fails to properly validate or sanitize symbolic link references, allowing malicious users to create or manipulate symbolic links that point to target files owned by different users. This occurs because the daemon does not adequately check the ownership or permissions of symbolic link targets before performing file operations, leading to a situation where a local attacker can redirect file operations to arbitrary locations within the file system. The vulnerability is classified under CWE-59 as improper link resolution, which is a well-documented weakness in file system security mechanisms that directly impacts the integrity of file operations.
From an operational perspective, this vulnerability creates a significant risk for multi-user systems where users may have varying privilege levels and where data isolation is critical. Local users can exploit this weakness to overwrite configuration files, executable binaries, or sensitive data files belonging to other users or system processes, potentially leading to privilege escalation or complete system compromise. The impact extends beyond simple file overwrites as attackers can target critical system files, log files, or user data repositories, making this vulnerability particularly dangerous in environments where multiple users share the same system resources. The attack requires only local access and basic user privileges, making it an attractive target for both malicious insiders and external attackers who have gained initial access to the system.
The exploitation of this vulnerability aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence. Attackers can leverage this weakness to establish backdoors or modify system configurations that maintain their access privileges across system reboots. The vulnerability also supports lateral movement techniques when combined with other local exploits, as attackers can use file overwrites to modify system binaries or configuration files that are executed by other users or system processes. Security professionals should note that this vulnerability demonstrates the importance of proper file system access controls and the need for comprehensive privilege separation mechanisms within system daemons. Organizations should implement robust monitoring for suspicious file system activities and ensure that all system daemons properly validate file references to prevent similar issues in other services.
Mitigation strategies for this vulnerability should focus on immediate patching of affected Debian systems, implementing proper file system permissions and access controls, and conducting comprehensive security audits of all system daemons. System administrators should also consider implementing mandatory access controls and file integrity monitoring solutions to detect unauthorized file modifications. The vulnerability highlights the critical importance of secure coding practices in system-level software development and emphasizes the need for thorough security testing of file system operations within daemon processes. Regular security assessments and privilege reviews should be conducted to identify and remediate similar weaknesses in other system components, as this type of vulnerability can often be found in poorly designed file handling mechanisms across various software platforms.