CVE-2003-0253 in HTTP Server
Summary
by MITRE
The prefork MPM in Apache 2 before 2.0.47 does not properly handle certain errors from accept, which could lead to a denial of service.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/23/2025
The vulnerability described in CVE-2003-0253 affects the prefork Multi-Processing Module (MPM) of Apache HTTP Server version 2.0.46 and earlier. This issue stems from improper error handling within the accept system call processing, which forms a critical component of the server's connection management mechanism. The prefork MPM operates by creating multiple child processes, each capable of handling individual client requests, making it essential for maintaining server availability and performance. When the accept function fails to properly manage specific error conditions, it creates a potential pathway for attackers to exploit the server's connection handling logic.
The technical flaw manifests when the accept system call encounters certain error states that are not adequately handled by the prefork MPM implementation. The accept function is responsible for accepting incoming network connections and establishing communication channels between the server and client applications. In vulnerable versions of Apache, when accept returns specific error codes or encounters exceptional conditions, the server fails to properly clean up resources or reset connection states. This improper error handling can lead to a scenario where the server becomes unresponsive or enters a degraded state where it cannot properly accept new connections.
The operational impact of this vulnerability creates a significant denial of service condition that can severely impact web server availability. Attackers can exploit this weakness by sending specially crafted requests or by creating network conditions that trigger the problematic error paths within the accept function. Once exploited, the vulnerability can cause the Apache server to stop accepting new connections, effectively rendering the web service unavailable to legitimate users. The impact extends beyond simple service interruption as the server may require manual intervention or restart to recover from the corrupted state, potentially causing extended downtime for critical web applications.
This vulnerability aligns with CWE-248, which addresses the issue of unhandled exceptions in software systems, and represents a classic example of improper error handling in network services. From an ATT&CK perspective, this weakness maps to the T1499.004 technique related to network denial of service attacks, where adversaries exploit application-level flaws to disrupt service availability. The vulnerability also demonstrates characteristics of T1566.001 related to phishing attacks, as attackers might use this service disruption as part of broader attack campaigns to mask malicious activities or create opportunities for additional exploitation.
Mitigation strategies for CVE-2003-0253 primarily involve upgrading to Apache HTTP Server version 2.0.47 or later, which contains the necessary patches to properly handle accept function errors. System administrators should also implement monitoring solutions to detect unusual connection patterns or service disruptions that might indicate exploitation attempts. Additionally, network-level protections such as rate limiting and connection tracking can help reduce the impact of potential attacks by limiting the number of concurrent connection attempts. Organizations should also consider implementing intrusion detection systems that can identify suspicious traffic patterns associated with this specific vulnerability. The fix implemented in Apache 2.0.47 addresses the root cause by ensuring proper error state management and resource cleanup when accept function encounters exceptional conditions, thereby preventing the denial of service scenario.