CVE-1999-0636 in Host
Summary
by MITRE
The discard service is running.
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Analysis
by VulDB Data Team • 03/20/2023
The discard service represents a fundamental network security vulnerability that has persisted across decades of internet infrastructure deployment. This service operates on port 9/tcp and functions as a simple network service that accepts data from clients but discards all received information without processing or storing it. The service exists purely for testing and debugging purposes within the internet protocol suite, designed to provide a reliable means of sending data to a black hole endpoint. However, its presence on production systems constitutes a significant security risk as it violates the principle of least privilege and provides an unnecessary attack surface that malicious actors can exploit. The service operates without authentication requirements, making it trivial for unauthorized users to connect and potentially consume system resources or use it as a vector for further attacks.
The technical flaw associated with the discard service stems from its default configuration on most operating systems, where it runs with elevated privileges and accepts connections from any network source. This implementation pattern violates security best practices established by organizations such as the Center for Internet Security and follows the ATT&CK framework's methodology for identifying network service vulnerabilities. The service can be exploited through various means including denial of service attacks where an attacker floods the service with data to consume system resources, or as a stepping stone for more sophisticated attacks. The service's design inherently lacks any form of access control or authentication mechanisms, making it a prime example of a service that should never be exposed to untrusted networks. According to CWE classification, this vulnerability falls under CWE-668, which describes "Exposure of Resource to Wrong Host," as the service provides access to system resources without proper host validation or access control measures.
The operational impact of running the discard service extends beyond simple resource consumption and represents a critical security gap in system configurations. When active on production systems, this service can be leveraged by attackers to perform reconnaissance activities, test network connectivity, or as part of larger attack campaigns. The service's presence creates a persistent entry point that network defenders must monitor and secure, consuming valuable time and resources that could be allocated to more critical security concerns. Organizations implementing the ATT&CK framework would classify this vulnerability under initial access techniques, specifically noting the service as a potential means for adversaries to establish footholds within networks. The service's default activation on most operating systems creates a situation where administrators may unknowingly leave vulnerable services running, violating the principle of defense in depth that security professionals advocate for.
Mitigation strategies for the discard service vulnerability require immediate administrative action to disable or remove the service from production systems. System administrators should implement comprehensive network segmentation policies that prevent access to unnecessary services and follow the principle of least privilege when configuring network services. The recommended approach includes disabling the discard service through proper system configuration management, removing the service from system startup routines, and ensuring that network access controls prevent external connections to port 9. Organizations should also implement regular security audits to identify and remediate similar vulnerabilities across their infrastructure, following guidelines established by the National Institute of Standards and Technology and other industry security frameworks. Additionally, network monitoring solutions should be configured to alert administrators when unexpected connections to this port occur, providing visibility into potential unauthorized access attempts. The implementation of these controls aligns with the MITRE ATT&CK framework's recommendations for securing network services and preventing unauthorized access to system resources.