CVE-2006-0734 in Half-Life CSTRIKE Dedicated Server
Summary
by MITRE
The SV_CheckForDuplicateNames function in Valve Software Half-Life CSTRIKE Dedicated Server 1.6 and earlier allows remote authenticated users to cause a denial of service (infinite loop and daemon hang) via a backslash character at the end of a connection string to UDP port 27015.
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Analysis
by VulDB Data Team • 03/28/2025
The vulnerability identified as CVE-2006-0734 represents a critical denial of service weakness in Valve Software Half-Life Counter-Strike Dedicated Server versions 1.6 and earlier. This flaw specifically targets the SV_CheckForDuplicateNames function which is responsible for validating player names during server connection processes. The vulnerability manifests when a remote authenticated user crafts a malicious connection string containing a backslash character at the end and directs it to the server's UDP port 27015. This seemingly simple character insertion triggers a pathological condition within the server's name validation logic that results in an infinite loop, effectively causing the server daemon to hang and become unresponsive to legitimate connection requests.
The technical mechanism behind this vulnerability stems from inadequate input validation within the SV_CheckForDuplicateNames function. When processing connection strings, the function fails to properly handle special characters including backslashes in a manner that could lead to recursive or iterative processing patterns. The backslash character at the end of a connection string creates a condition where the validation routine enters an infinite loop while attempting to parse and check for duplicate names, as the backslash character is not properly escaped or handled in the string processing logic. This type of vulnerability aligns with CWE-835, which specifically addresses infinite loops or iterations in software systems, making it particularly dangerous in networked server environments where continuous availability is critical for legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption to create significant challenges for server administrators and legitimate players. When exploited, the infinite loop causes the dedicated server daemon to become unresponsive, preventing new players from connecting while potentially disconnecting existing players. This denial of service condition effectively renders the game server unusable until the server process is manually terminated and restarted. The vulnerability is particularly concerning because it requires only authenticated access to exploit, meaning that users who have already gained some level of access to the server environment can trigger this condition. From an attacker's perspective, this represents a low-effort, high-impact method of disrupting server operations, making it a favored technique for those seeking to compromise server availability.
Mitigation strategies for this vulnerability should focus on immediate patch application from Valve Software, as the company released updates addressing this specific issue in later versions of their dedicated server software. Network administrators should implement proper access controls to limit authentication privileges to only authorized users, reducing the attack surface for potential exploitation. Additionally, implementing monitoring solutions that can detect anomalous connection patterns or prolonged daemon hang conditions can provide early warning of exploitation attempts. The vulnerability demonstrates the importance of proper input validation and the potential for seemingly benign characters to trigger catastrophic system behavior. This case study aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and highlights the need for robust error handling in network service implementations. Server administrators should also consider implementing automated restart mechanisms for critical services and maintaining regular backups to ensure quick recovery from such incidents.