CVE-2003-0251 in NIS Server
Summary
by MITRE
ypserv NIS server before 2.7 allows remote attackers to cause a denial of service via a TCP client request that does not respond to the server, which causes ypserv to block.
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Analysis
by VulDB Data Team • 08/21/2025
The vulnerability described in CVE-2003-0251 affects the ypserv NIS (Network Information Service) server version 2.6 and earlier, representing a classic denial of service weakness in network services. This issue specifically targets the TCP client request handling mechanism within the NIS server implementation, creating a condition where the server becomes unresponsive due to its inability to properly manage client connections. The flaw exists in the server's protocol handling logic, where it fails to implement proper timeout mechanisms or connection state management when dealing with non-responsive client requests.
The technical nature of this vulnerability stems from the ypserv server's blocking behavior when processing TCP connections that fail to respond appropriately to server requests. According to CWE-400, this represents a resource management issue where the server's thread or process becomes indefinitely blocked while waiting for a response that will never arrive. The vulnerability operates at the application layer of the network stack, specifically within the NIS server's TCP handling routines, making it particularly dangerous in environments where NIS services are critical for system authentication and configuration management. The server's design assumes that all connected clients will properly respond to server requests, but when this assumption fails, the service enters a state where it cannot process subsequent requests.
The operational impact of this vulnerability extends beyond simple service disruption, as NIS servers typically provide critical functions including user authentication, group membership information, and system configuration data across networked environments. When ypserv becomes blocked due to non-responsive client connections, legitimate users and systems attempting to access NIS services experience complete service unavailability. This can cascade into broader network outages, particularly in environments where multiple systems depend on NIS for authentication and authorization. The vulnerability is particularly concerning in enterprise environments where NIS servers serve as foundational infrastructure components for user management and system configuration, as the denial of service can effectively disable authentication services across large network segments.
Mitigation strategies for this vulnerability should focus on implementing proper timeout mechanisms and connection state management within the ypserv server configuration. Organizations should upgrade to ypserv version 2.7 or later, which includes fixes for this blocking behavior. Network administrators should also consider implementing connection timeout parameters and monitoring mechanisms to detect and automatically terminate hanging connections. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service, emphasizing the importance of proper resource management and connection handling in preventing such attacks. Additionally, implementing network segmentation and access controls can limit the potential impact of such attacks by restricting direct access to NIS servers from untrusted networks, while also ensuring that proper logging and alerting mechanisms are in place to detect unusual connection patterns that might indicate exploitation attempts.