CVE-2002-0381 in OpenBSD
Summary
by MITRE
The TCP implementation in various BSD operating systems (tcp_input.c) does not properly block connections to broadcast addresses, which could allow remote attackers to bypass intended filters via packets with a unicast link layer address and an IP broadcast address.
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Analysis
by VulDB Data Team • 06/07/2018
The vulnerability described in CVE-2002-0381 represents a critical flaw in the Transmission Control Protocol implementation across multiple BSD operating systems, specifically within the tcp_input.c source file. This weakness stems from insufficient validation mechanisms that fail to properly enforce connection restrictions when dealing with broadcast addresses. The flaw allows malicious actors to exploit a fundamental network protocol implementation error that could undermine security measures designed to prevent unauthorized access through broadcast communication channels.
The technical root cause of this vulnerability lies in the improper handling of IP broadcast addresses within the TCP connection establishment process. When network packets arrive with unicast link layer addresses but contain broadcast IP addresses, the system fails to adequately validate these conflicting address types. This creates a scenario where attackers can craft packets that appear to originate from legitimate unicast addresses while targeting broadcast destinations, effectively bypassing standard network filtering mechanisms. The vulnerability specifically affects the tcp_input.c module which processes incoming TCP segments and manages connection states, making it a core component of the network stack's security posture.
From an operational perspective, this vulnerability presents significant risks to systems running affected BSD variants including FreeBSD, OpenBSD, and NetBSD. Attackers can exploit this weakness to establish unauthorized connections to broadcast addresses, potentially enabling various malicious activities such as network reconnaissance, denial of service attacks, or exploitation of other network services. The impact extends beyond simple connection bypassing since broadcast addresses are often used for network discovery and service announcement protocols, making this vulnerability particularly dangerous in environments where such communication patterns are common. The flaw essentially allows attackers to circumvent network access controls that should prevent connections to broadcast addresses, creating potential entry points for further exploitation.
The vulnerability maps to CWE-622, which specifically addresses improper restriction of operations within a security domain, and aligns with ATT&CK technique T1071.004 for application layer protocol usage. The security implications extend to network segmentation breaches, as the flaw enables attackers to potentially access network services that should only be reachable through unicast communication. Organizations running affected systems face the risk of unauthorized network scanning, service disruption, and potential compromise of network infrastructure. The vulnerability's exploitation requires minimal privileges and can be executed remotely, making it particularly attractive to threat actors seeking to establish persistent network access or conduct reconnaissance activities.
Mitigation strategies should include implementing proper network filtering at the firewall level to block incoming packets with broadcast IP addresses, particularly those that conflict with unicast link layer addresses. System administrators should update to patched versions of their BSD operating systems and apply security patches that correct the tcp_input.c implementation. Network segmentation and monitoring should be enhanced to detect anomalous traffic patterns involving broadcast addresses. The implementation of strict ingress filtering rules and proper validation of address combinations within network protocols provides the most effective defense against this particular vulnerability. Regular security audits of network stack implementations and proactive monitoring of system logs for unusual connection patterns remain essential defensive measures.