CVE-2000-0128 in The Finger Server
Summary
by MITRE
The Finger Server 0.82 allows remote attackers to execute commands via shell metacharacters.
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Analysis
by VulDB Data Team • 07/24/2024
The vulnerability identified as CVE-2000-0128 affects the Finger Server version 0.82, which represents a critical security flaw in network services that has persisted for decades. This vulnerability resides in the server's handling of user input through the finger protocol, a legacy network service designed to provide user information on remote systems. The finger protocol operates on TCP port 79 and was historically used for identifying users on network systems. The specific flaw in version 0.82 occurs when the server fails to properly sanitize input received from remote clients, creating an avenue for arbitrary command execution through shell metacharacters.
The technical implementation of this vulnerability stems from improper input validation and sanitization within the finger server's processing logic. When a remote attacker sends specially crafted input containing shell metacharacters such as semicolons, pipes, or backticks, the server interprets these characters as command separators rather than literal input. This occurs because the server executes user-supplied input directly through shell commands without proper escaping or filtering mechanisms. The vulnerability maps directly to CWE-78, known as "Improper Neutralization of Special Elements used in an OS Command," which is a fundamental weakness in command execution systems where user input is not properly sanitized before being passed to operating system commands.
From an operational perspective, this vulnerability presents a severe risk to network security infrastructure as it allows remote attackers to execute arbitrary commands on the affected system with the privileges of the finger server process. The impact extends beyond simple command execution to potentially provide attackers with complete system compromise, including privilege escalation, data exfiltration, and persistence mechanisms. Attackers can leverage this vulnerability to gain unauthorized access to sensitive information, install backdoors, or launch further attacks against the internal network. The vulnerability's remote nature means that attackers do not require physical access or prior authentication to exploit the flaw, making it particularly dangerous in networked environments.
The exploitation of this vulnerability aligns with several techniques documented in the MITRE ATT&CK framework, specifically mapping to T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1068 for "Exploitation for Privilege Escalation." The attack chain typically involves initial reconnaissance to identify vulnerable systems, followed by crafting malicious input that triggers the command injection. Organizations running finger servers are particularly at risk since this service is often enabled by default on many Unix-like systems, and the protocol has been largely deprecated in favor of more secure alternatives. Security professionals should note that this vulnerability represents a classic example of how legacy services can pose significant security risks when not properly maintained or secured.
Mitigation strategies for CVE-2000-0128 should include immediate discontinuation of the finger service if not absolutely required for legacy applications, as the service has been deprecated for over two decades. Organizations should implement network segmentation to isolate systems running finger services and deploy firewall rules to block traffic on port 79. The recommended remediation involves upgrading to a secure version of the finger server software or replacing it entirely with modern authentication and user information services. Additionally, implementing proper input validation and sanitization measures, such as using allowlists for acceptable input characters and proper shell escaping techniques, would prevent similar vulnerabilities in other applications. System administrators should also consider implementing intrusion detection systems to monitor for suspicious finger protocol activity and conduct regular vulnerability assessments to identify other deprecated services that may pose similar risks.