CVE-2000-1167 in FreeBSD
Summary
by MITRE
ppp utility in FreeBSD 4.1.1 and earlier does not properly restrict access as specified by the "nat deny_incoming" command, which allows remote attackers to connect to the target system.
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Analysis
by VulDB Data Team • 02/13/2017
The vulnerability described in CVE-2000-1167 represents a significant security flaw in the ppp (Point-to-Point Protocol) utility implementation within FreeBSD operating systems version 4.1.1 and earlier. This issue specifically affects network security configurations that rely on the nat deny_incoming command for controlling incoming network connections. The ppp utility serves as a critical component for establishing and managing point-to-point network connections, particularly in dial-up and broadband scenarios where network address translation and firewall rules must be carefully enforced to maintain system security boundaries.
The technical flaw manifests in the improper enforcement of access restrictions when the nat deny_incoming command is configured within the ppp utility. This command is designed to prevent incoming connections from reaching the target system, but due to implementation errors in the affected FreeBSD versions, the restriction mechanism fails to properly enforce these access controls. The vulnerability essentially creates a pathway for remote attackers to bypass the intended network filtering mechanisms and establish unauthorized connections to systems configured with this security feature. This represents a classic case of insufficient access control enforcement, which falls under the broader category of CWE-284 Access Control Flaws that specifically addresses improper access control implementations in network security contexts.
The operational impact of this vulnerability extends beyond simple network connectivity issues, as it fundamentally undermines the security posture of systems relying on ppp for network access management. Remote attackers can exploit this weakness to gain unauthorized access to systems that should be protected by the nat deny_incoming configuration, potentially leading to complete system compromise. The vulnerability affects the core network security model implemented by the ppp utility, creating a persistent backdoor that remains active as long as the affected software version is in use. This type of flaw particularly impacts organizations relying on FreeBSD for network infrastructure, as it compromises the integrity of their firewall configurations and allows attackers to circumvent network security controls that should prevent unauthorized incoming connections.
Security practitioners should understand that this vulnerability aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, where network protocol implementations can be exploited to bypass security controls. The flaw essentially allows attackers to perform network reconnaissance and connection establishment that should have been blocked by the nat deny_incoming command. Organizations should implement immediate mitigation strategies including upgrading to FreeBSD versions that address this vulnerability, implementing additional network segmentation measures, and monitoring for unauthorized network connections. The vulnerability also highlights the importance of proper input validation and access control enforcement in network security utilities, as it demonstrates how a single implementation error in a core networking component can create significant security risks that persist across network configurations and user environments.