CVE-2001-0969 in FreeBSD
Summary
by MITRE
ipfw in FreeBSD does not properly handle the use of "me" in its rules when point to point interfaces are used, which causes ipfw to allow connections from arbitrary remote hosts.
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Analysis
by VulDB Data Team • 02/11/2017
The vulnerability described in CVE-2001-0969 affects the ipfw packet filtering framework in FreeBSD operating systems, specifically when utilizing the "me" keyword within firewall rules on point-to-point network interfaces. This flaw represents a significant security weakness in network access control mechanisms that can lead to unauthorized network access and potential compromise of protected systems. The issue arises from improper handling of interface addressing when the "me" keyword is employed in firewall rule configurations, creating a bypass condition that undermines the intended security posture.
The technical root cause of this vulnerability stems from how ipfw processes the "me" keyword in firewall rules when dealing with point-to-point interfaces such as ppp or sl interfaces. In normal operation, the "me" keyword should resolve to the local interface address, but in this specific scenario, the implementation fails to properly validate or restrict the address resolution process. When point-to-point interfaces are configured, the network stack may present ambiguous addressing information that ipfw does not correctly interpret, leading to the acceptance of connections from remote hosts that should have been blocked. This behavior violates fundamental principles of network access control and creates a path for unauthorized network traffic to traverse the firewall.
The operational impact of this vulnerability is substantial as it allows remote attackers to bypass firewall restrictions that were specifically designed to prevent unauthorized access to network resources. An attacker could potentially establish connections to systems behind the firewall that would normally be protected by ipfw rules, effectively neutralizing the security controls in place. This vulnerability particularly affects environments where point-to-point connections are utilized for network connectivity, such as dial-up connections, serial line interfaces, or VPN tunnels. The consequence is that any service or application protected by ipfw rules could become accessible to remote hosts, potentially leading to data breaches, system compromise, or unauthorized access to sensitive network resources.
This vulnerability aligns with CWE-284, which addresses improper access control in network security implementations, and represents a classic case of privilege escalation through configuration flaws in network security controls. The issue also maps to ATT&CK technique T1046, which involves network service scanning and access to network resources that should be protected. Organizations using FreeBSD systems with ipfw firewall configurations and point-to-point interfaces are particularly at risk, as the vulnerability can be exploited without requiring elevated privileges or specialized knowledge beyond understanding basic network security concepts. The exploitability of this vulnerability is relatively straightforward since it only requires proper network configuration and knowledge of the ipfw rule syntax.
The recommended mitigation strategies include immediate patching of affected FreeBSD systems with the appropriate security updates that address the ipfw handling of the "me" keyword in point-to-point interface contexts. Administrators should also consider implementing additional network segmentation controls and monitoring for unauthorized access attempts. Alternative firewall implementations or rule configurations that avoid the problematic "me" keyword usage should be considered as temporary measures while permanent fixes are implemented. Regular security auditing of firewall configurations and network access controls is essential to identify similar vulnerabilities and maintain robust network security posture. The vulnerability highlights the importance of thorough testing of security controls in various network interface configurations and demonstrates the critical need for proper input validation in network security implementations.