CVE-2006-6947 in MultiWriter 1700C
Summary
by MITRE
The FTP server in the NEC MultiWriter 1700C allows remote attackers to redirect traffic to other sites (aka FTP bounce) via the PORT command, a variant of CVE-1999-0017.
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Analysis
by VulDB Data Team • 04/12/2019
The vulnerability identified as CVE-2006-6947 affects the NEC MultiWriter 1700C FTP server implementation and represents a critical security flaw that enables remote attackers to perform FTP bounce attacks through manipulation of the PORT command. This vulnerability is classified as a variant of CVE-1999-0017, which established the foundational understanding of FTP bounce attacks within the cybersecurity community. The NEC MultiWriter 1700C device operates as an FTP server that handles file transfer operations, and the specific flaw lies in how it processes the PORT command during FTP connections. When an attacker sends a PORT command to the server, the device fails to properly validate the destination address, allowing malicious redirection of traffic to arbitrary external systems.
The technical implementation of this vulnerability stems from improper input validation within the FTP server's command processing logic. The PORT command in FTP is designed to specify the IP address and port number where the data connection should be established, typically used for active FTP mode operations. However, the NEC MultiWriter 1700C fails to validate whether the destination address provided in the PORT command is legitimate or whether it represents a redirection attempt. This validation gap creates an opportunity for attackers to specify alternate IP addresses that the FTP server will use for subsequent data connections, effectively enabling traffic redirection to unintended destinations.
The operational impact of this vulnerability extends beyond simple traffic redirection, as it can facilitate various malicious activities including data exfiltration, command execution, and network reconnaissance. Attackers can leverage this flaw to bypass network security controls that might be in place to restrict direct connections to certain external systems. The vulnerability creates a pathway for attackers to establish connections through the compromised FTP server to systems that would otherwise be inaccessible from the attacker's network position. This capability aligns with the attack pattern described in the MITRE ATT&CK framework under the technique of "Proxy Usage" and represents a form of network tunneling that can circumvent traditional firewall and intrusion detection system protections.
Security professionals should note that this vulnerability operates at the application layer and can be particularly dangerous in environments where FTP servers are used to transfer sensitive data. The flaw demonstrates a classic example of inadequate input sanitization that is categorized under CWE-20, which covers "Improper Input Validation" in the Common Weakness Enumeration catalog. Organizations using NEC MultiWriter 1700C devices should implement immediate mitigations including disabling the PORT command functionality, implementing proper network segmentation, and applying firewall rules that restrict FTP server access to trusted networks only. Additionally, network monitoring should be enhanced to detect unusual FTP traffic patterns that might indicate exploitation attempts. The vulnerability also underscores the importance of regular security assessments and the need for comprehensive patch management programs that address legacy systems with known security flaws.
This vulnerability serves as a reminder of the persistent challenges associated with maintaining security in legacy network infrastructure. The fact that this issue was discovered in 2006 and represents a variant of a vulnerability from 1999 highlights the longevity of certain security flaws in enterprise environments. Organizations should prioritize the identification and remediation of similar vulnerabilities across their entire network infrastructure, particularly in systems that continue to operate without regular security updates or modernization efforts. The NEC MultiWriter 1700C represents a system that likely predates modern security standards and best practices, making it particularly vulnerable to exploitation techniques that have been well-documented and understood for over two decades.