CVE-2002-0964 in Half-Life
Summary
by MITRE
Half-Life Server 1.1.1.0 and earlier allows remote attackers to cause a denial of service (resource exhaustion) via multiple responses to the initial challenge with different cd_key values, which reaches the player limit and prevents other players from connecting until the original responses have timed out.
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Analysis
by VulDB Data Team • 12/19/2024
The vulnerability identified as CVE-2002-0964 affects Half-Life Server version 1.1.1.0 and earlier implementations, representing a classic resource exhaustion attack vector that exploits the server's connection handling mechanism. This issue stems from the server's insufficient validation of challenge response sequences during the authentication process, creating a scenario where malicious actors can manipulate the connection state machine to consume available resources. The flaw specifically targets the server's player slot management system, which operates under the assumption that legitimate challenge responses will be processed in a timely and orderly fashion. When multiple challenge responses are sent with varying cd_key values, the server maintains these connections in a pending state, effectively consuming available player slots that should remain free for legitimate users.
The technical execution of this attack involves sending multiple challenge responses to the server's authentication endpoint, each containing different cd_key values that do not correspond to valid player sessions. This technique exploits a fundamental design weakness in the server's connection lifecycle management, where the system fails to properly terminate or timeout these invalid connection attempts. The vulnerability manifests as a denial of service condition that can be triggered remotely without requiring authentication or privileged access. The server's architecture maintains these pseudo-connections in memory until their natural timeout occurs, which can extend for several minutes, effectively locking out legitimate players from joining the game. This type of attack falls under the category of resource exhaustion as defined by common weakness enumeration CWE-400, specifically targeting the server's ability to manage concurrent connections and allocate player slots effectively.
The operational impact of CVE-2002-0964 extends beyond simple service disruption, as it represents a significant security concern for game servers that rely on player slot management for operational integrity. The vulnerability can be exploited by any remote attacker with network access to the server, making it particularly dangerous in multiplayer gaming environments where server availability directly impacts user experience and community engagement. Attackers can maintain persistent resource exhaustion conditions for extended periods, potentially disrupting gaming sessions and affecting server performance for legitimate users. The attack demonstrates a clear violation of the principle of least privilege and proper resource management, as the server fails to implement adequate rate limiting or connection state validation. This vulnerability also aligns with attack techniques documented in the attack pattern taxonomy where adversaries leverage protocol implementation weaknesses to consume server resources, specifically targeting the connection management layer of the application.
Mitigation strategies for this vulnerability require immediate implementation of connection rate limiting and improved challenge response validation mechanisms within the server software. Administrators should implement network-level filtering to limit the number of challenge responses that can be processed from a single source within a given time window, effectively preventing the accumulation of pending connections. The server should be configured with aggressive timeout values for pending challenge responses to ensure that invalid connections do not persist indefinitely. Additionally, implementing proper authentication sequence validation that rejects duplicate or invalid cd_key values during the challenge phase can prevent the accumulation of pseudo-connections. System administrators should also monitor server resource utilization and connection states to detect anomalous patterns that may indicate exploitation attempts. The vulnerability highlights the importance of robust input validation and proper resource management in networked applications, particularly those handling user authentication and connection state management. Regular updates and patches should be implemented to address such implementation flaws, as the original version of Half-Life Server contained insufficient protections against this type of resource exhaustion attack pattern.