CVE-2000-0916 in FreeBSD
Summary
by MITRE
FreeBSD 4.1.1 and earlier, and possibly other BSD-based OSes, uses an insufficient random number generator to generate initial TCP sequence numbers (ISN), which allows remote attackers to spoof TCP connections.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2000-0916 represents a critical weakness in the TCP/IP stack implementation of FreeBSD versions 4.1.1 and earlier, as well as potentially other BSD-based operating systems. This flaw directly impacts the fundamental security mechanism of network communications by compromising the generation of initial sequence numbers that are essential for TCP connection establishment and integrity. The issue stems from the use of a weak random number generator that fails to provide adequate entropy for generating unpredictable sequence values, creating a pathway for sophisticated network attacks.
The technical flaw manifests in the insufficient randomness of the initial TCP sequence number generation process, which is a core component of the Transmission Control Protocol's security architecture. According to CWE-330, this vulnerability falls under the category of using insufficiently random values, where the weakness lies in the cryptographic randomness implementation rather than the network protocol itself. The vulnerability specifically targets the TCP three-way handshake mechanism, where an attacker can predict or guess the initial sequence number that a system will use for establishing new connections. This weakness enables attackers to perform TCP sequence number prediction attacks, which are classified under the MITRE ATT&CK technique T1071.004 for application layer protocol and T1566 for credential access through network sniffing.
The operational impact of this vulnerability is severe and far-reaching, as it allows remote attackers to completely bypass the TCP connection integrity verification process. An attacker who successfully predicts the initial sequence number can inject malicious data into existing TCP connections, perform session hijacking, or establish fraudulent connections to network services without proper authentication. This capability undermines the core security assumptions of TCP communications and can lead to complete system compromise, data interception, and unauthorized access to network resources. The vulnerability affects the confidentiality, integrity, and availability of network services by enabling man-in-the-middle attacks that can go undetected by traditional network monitoring systems.
Mitigation strategies for this vulnerability require immediate system updates and patches to address the weak random number generator implementation. Organizations should prioritize upgrading to FreeBSD versions that incorporate improved entropy sources and cryptographic random number generation algorithms. The implementation of additional network security measures such as TCP sequence number randomization, connection tracking mechanisms, and network intrusion detection systems can provide layered protection against exploitation attempts. System administrators should also consider implementing network segmentation, firewall rules, and monitoring solutions that can detect anomalous TCP sequence number patterns that might indicate exploitation attempts. According to industry best practices for secure system configuration, this vulnerability highlights the critical importance of proper entropy collection and cryptographic implementation in network security systems, emphasizing the need for robust random number generation as a fundamental security prerequisite for all network protocols.