CVE-2001-0309 in Linux
Summary
by MITRE
inetd in Red Hat 6.2 does not properly close sockets for internal services such as chargen, daytime, echo, etc., which allows remote attackers to cause a denial of service via a series of connections to the internal services.
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Analysis
by VulDB Data Team • 05/16/2019
The vulnerability described in CVE-2001-0309 represents a critical denial of service flaw within the inetd service daemon on Red Hat Enterprise Linux 6.2 systems. This issue specifically targets the socket management behavior of inetd when handling internal network services such as chargen, daytime, and echo protocols. The fundamental problem lies in the improper socket closure mechanism that occurs when these services are invoked through the inetd daemon, creating a condition where socket resources remain allocated even after service completion. This architectural weakness enables malicious actors to exploit the vulnerability by establishing multiple sequential connections to these internal services, ultimately exhausting available socket resources and rendering the system incapable of accepting new connections for these services. The flaw directly impacts the availability aspect of the system's security posture, as it allows remote attackers to disrupt normal service operations without requiring elevated privileges or complex exploitation techniques.
The technical implementation of this vulnerability stems from the inetd daemon's failure to properly manage socket lifecycle events during the execution of internal services. When a client connects to services like chargen, daytime, or echo, the inetd daemon forks a new process to handle the connection but fails to ensure complete socket cleanup upon process termination. This results in socket file descriptors remaining in a closed state but still referenced by the system, creating a resource leak that accumulates over time. The specific nature of this flaw aligns with CWE-404, which describes improper resource management where a program fails to release or properly close resources, and CWE-119, which addresses weaknesses in memory management that can lead to resource exhaustion. The vulnerability operates at the network protocol level and demonstrates a classic example of resource exhaustion attacks that target daemon processes responsible for handling multiple concurrent connections.
The operational impact of CVE-2001-0309 extends beyond simple service disruption to potentially compromise system availability and reliability. When exploited, the vulnerability can cause cascading effects throughout the network infrastructure as affected services become unresponsive, leading to broader operational degradation. System administrators may experience increased system load due to the accumulation of zombie processes and unreleased socket resources, while legitimate users attempting to access these services will encounter connection failures. The attack vector is particularly concerning as it requires minimal technical expertise to execute, making it accessible to a wide range of threat actors including script kiddies and automated attack tools. This vulnerability directly maps to ATT&CK technique T1499.004, which describes network denial of service attacks that target availability by exhausting system resources, and T1071.004, which covers application layer protocol usage for command and control communications that can be leveraged for resource exhaustion attacks.
Mitigation strategies for CVE-2001-0309 should focus on both immediate patching and long-term architectural improvements to system security. The most effective immediate solution involves applying the vendor-provided security patches that address the socket management behavior in the inetd daemon implementation. System administrators should also implement connection rate limiting and monitoring mechanisms to detect unusual connection patterns that may indicate exploitation attempts. Network segmentation and firewall rules can be configured to restrict access to these internal services from untrusted networks, reducing the attack surface. Additionally, implementing proper service monitoring and alerting systems can help detect when socket resources are approaching exhaustion levels. The vulnerability highlights the importance of proper resource management in daemon implementations and serves as a reminder that even seemingly benign services can pose significant security risks when not properly engineered for robust resource handling. Organizations should also consider migrating away from legacy inetd implementations toward more modern service management frameworks that provide better resource isolation and cleanup mechanisms.