CVE-1999-0074 in Linux
Summary
by MITRE
Listening TCP ports are sequentially allocated, allowing spoofing attacks.
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Analysis
by VulDB Data Team • 04/16/2026
This vulnerability stems from the predictable allocation of TCP port numbers on systems that listen for incoming connections. The flaw occurs when a system sequentially assigns listening TCP ports to services, creating a pattern that can be easily anticipated by attackers. The vulnerability is classified under CWE-1220 which deals with predictable port allocation, and aligns with ATT&CK technique T1071.1004 for application layer protocol: DNS. The sequential allocation of ports creates a window of opportunity for attackers to perform spoofing attacks by predicting and targeting specific port numbers before they are assigned to legitimate services.
The technical implementation of this vulnerability relies on the fundamental TCP/IP protocol behavior where systems typically assign listening ports in ascending order starting from a predefined range. When a system starts services or accepts incoming connections, it often allocates ports sequentially, making the port assignment predictable to anyone who can monitor the system's port allocation process. This predictability allows attackers to perform port scanning and service discovery more efficiently, as they can infer which ports will be assigned to which services. The vulnerability is particularly concerning because it affects the fundamental security assumptions of network services and creates opportunities for man-in-the-middle attacks, port hijacking, and service impersonation.
The operational impact of this vulnerability extends beyond simple port prediction to encompass broader network security implications. Attackers can exploit this weakness to conduct reconnaissance more effectively, potentially gaining unauthorized access to systems by targeting services that are about to be assigned specific ports. This vulnerability undermines the security of network services by making them more accessible to unauthorized parties who can predict and target specific listening endpoints. The impact is particularly severe in environments where services are frequently restarted or where port allocation patterns are consistent across multiple systems, as attackers can systematically target these predictable port assignments to compromise multiple systems.
Mitigation strategies for this vulnerability should focus on implementing non-predictable port assignment mechanisms and enhancing overall network security posture. Systems should utilize randomized port allocation techniques where possible, ensuring that listening ports are assigned from a random range rather than following sequential patterns. Network administrators should implement proper port scanning controls and monitoring to detect unauthorized port access attempts. The solution approach aligns with security best practices outlined in NIST SP 800-53 and ISO 27001 standards, which emphasize the importance of unpredictable resource allocation to prevent exploitation of predictable patterns. Additional controls such as firewall rules, intrusion detection systems, and network segmentation can help mitigate the risks associated with predictable port assignments by limiting access to critical services and monitoring for suspicious port access patterns.