CVE-2005-2239 in oftpd
Summary
by MITRE
oftpd 0.3.7 allows remote attackers to cause a denial of service via a USER command with a large number of null (\0) characters.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability identified as CVE-2005-2239 affects oftpd version 0.3.7, a lightweight ftp daemon implementation that was widely used in embedded systems and network appliances during the mid-2000s. This particular flaw represents a classic buffer over-read condition that occurs when the ftp daemon processes user authentication commands. The vulnerability specifically manifests when a remote attacker sends a USER command containing an excessive number of null characters, which the daemon fails to properly validate or sanitize before processing. This type of vulnerability falls under the category of improper input validation and can be classified as CWE-121, which deals with stack-based buffer overflow conditions. The flaw demonstrates a fundamental weakness in the input handling mechanisms of the ftp daemon, where the system does not adequately check the length or content of incoming authentication parameters.
The technical exploitation of this vulnerability occurs at the protocol level where the ftp daemon receives the USER command from a remote client. When the daemon processes this command, it attempts to parse and validate the username provided by the attacker, but fails to properly handle the excessive null character sequence. The null characters cause the daemon to misinterpret the input data structure, leading to a memory access violation or improper memory management that results in the daemon crashing. This behavior is consistent with CWE-125, which describes out-of-bounds read conditions, and represents a form of resource exhaustion that can be leveraged for denial of service attacks. The vulnerability is particularly concerning because it requires no authentication to exploit and can be triggered by any remote attacker with network access to the ftp service port, typically port 21.
The operational impact of this vulnerability extends beyond simple service disruption as it can be weaponized to create persistent denial of service conditions against ftp services. When exploited successfully, the vulnerability causes the oftpd daemon to terminate unexpectedly, requiring manual intervention to restart the service and restore ftp functionality. This can have significant implications for network infrastructure that relies on ftp services for file transfers, system administration, or automated processes. The vulnerability is particularly dangerous in embedded environments where ftp services are often used for firmware updates or system maintenance, as it can prevent legitimate administrative access to affected devices. Organizations using oftpd 0.3.7 should consider this vulnerability as part of their broader attack surface assessment, particularly in environments where ftp services are exposed to untrusted networks or where the service is used for critical infrastructure operations.
The mitigation strategy for CVE-2005-2239 involves immediate patching of the oftpd daemon to a version that properly validates input parameters and sanitizes user commands before processing. System administrators should also implement network-level controls such as firewall rules that limit access to ftp ports to trusted networks only, and consider disabling ftp services entirely if alternative secure protocols like sftp or scp are available. Additionally, network monitoring should be enhanced to detect unusual patterns of USER command traffic that may indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving denial of service attacks and service disruption, specifically T1499.004 which covers network disruption and T1566.002 which involves phishing with malicious attachments that may be used to gain initial access to systems running vulnerable ftp services. Organizations should also consider implementing intrusion detection systems that can identify and alert on malformed ftp commands containing excessive null characters. The vulnerability serves as a reminder of the importance of input validation and proper error handling in network services, particularly those that are exposed to untrusted network environments where they may be subject to various forms of malicious input injection attacks.