CVE-2003-0254 in HTTP Server
Summary
by MITRE
Apache 2 before 2.0.47, when running on an IPv6 host, allows attackers to cause a denial of service (CPU consumption by infinite loop) when the FTP proxy server fails to create an IPv6 socket.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/23/2025
The vulnerability described in CVE-2003-0254 represents a critical denial of service flaw affecting Apache HTTP Server version 2.0.47 and earlier when operating in IPv6 environments with FTP proxy functionality enabled. This issue stems from a fundamental design flaw in how the server handles socket creation failures within its FTP proxy module, creating a condition where malformed or unexpected network requests can trigger infinite loop behavior in the processing logic.
The technical root cause of this vulnerability lies in the Apache server's handling of IPv6 socket creation within its FTP proxy implementation. When the server attempts to establish an IPv6 socket connection and encounters a failure condition, the internal error handling mechanism contains a flaw that causes the system to enter an infinite loop rather than properly terminating or gracefully handling the error condition. This occurs specifically within the proxy server's network communication handling code where the failure to create an IPv6 socket triggers a recursive or iterative process that never completes, consuming 100% of available CPU resources.
The operational impact of this vulnerability extends beyond simple service disruption to create a complete system compromise scenario. An attacker can exploit this weakness by sending carefully crafted requests to the Apache server that force it to attempt IPv6 socket creation, thereby triggering the infinite loop condition. This results in sustained high CPU utilization that can effectively render the server unusable for legitimate requests, creating a denial of service condition that can persist until the server is manually restarted or the system is rebooted. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication or special privileges, making it a significant threat to web server availability.
This vulnerability aligns with CWE-835, which specifically addresses infinite loops or iterations that can lead to denial of service conditions. The flaw demonstrates poor error handling practices and inadequate boundary condition checking in network socket operations, which are fundamental security requirements. From an attack framework perspective, this vulnerability maps to the denial of service category within the MITRE ATT&CK framework, specifically under the technique of "Resource Exhaustion" where attackers consume system resources to prevent legitimate use of services.
The primary mitigation strategy involves upgrading to Apache HTTP Server version 2.0.47 or later, which contains the patched code that properly handles IPv6 socket creation failures without entering infinite loops. Additionally, system administrators should consider disabling FTP proxy functionality if it is not essential for operations, as this removes the attack surface entirely. Network monitoring should be implemented to detect unusual CPU consumption patterns that might indicate exploitation attempts, and firewalls can be configured to limit access to FTP proxy functionality where possible. The vulnerability also highlights the importance of thorough testing of network protocol handling code, particularly in dual-stack environments where both IPv4 and IPv6 capabilities must be properly managed to prevent similar issues in other software components.