CVE-2003-1581 in HTTP Server
Summary
by MITRE
The Apache HTTP Server 2.0.44, when DNS resolution is enabled for client IP addresses, allows remote attackers to inject arbitrary text into log files via an HTTP request in conjunction with a crafted DNS response, as demonstrated by injecting XSS sequences, related to an "Inverse Lookup Log Corruption (ILLC)" issue.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability described in CVE-2003-1581 represents a critical security flaw in the Apache HTTP Server version 2.0.44 that stems from improper handling of DNS resolution during client identification processes. This issue specifically manifests when the server is configured to perform inverse DNS lookups to resolve client IP addresses into hostnames for logging purposes, creating a dangerous intersection between network resolution mechanisms and logging functionality that adversaries can exploit to manipulate server logs.
The technical flaw exploits the fundamental trust placed in DNS resolution responses within the logging pipeline of the Apache server. When a client connects to the server, the system attempts to perform a reverse DNS lookup to determine the client's hostname, which is then recorded in the access logs. The vulnerability occurs because the server does not properly sanitize or validate the DNS response data before incorporating it into log entries, allowing malicious actors to craft DNS responses that contain specially formatted text including cross-site scripting sequences. This creates a scenario where the attacker can inject arbitrary content into the server's log files through legitimate HTTP requests that trigger the DNS resolution process.
The operational impact of this vulnerability extends beyond simple log corruption, as it enables attackers to potentially hide malicious activities within server logs or inject content that could be interpreted by log analysis tools or web applications that process these logs. The injection of XSS sequences into log files can create persistent security risks when these logs are later viewed by administrators or processed by automated systems, as the malicious content could execute within web browsers or other log viewing applications. This represents a sophisticated attack vector that leverages the legitimate logging functionality to create a covert channel for malicious payload delivery and operational persistence.
This vulnerability aligns with CWE-116, which addresses the improper encoding or escaping of output, and demonstrates characteristics consistent with the ATT&CK technique T1070.006 for "Indicator Removal on Host: Log Writing", where adversaries manipulate system logs to obscure their activities. The flaw also relates to the broader category of input validation issues that affect web server configurations, particularly those involving external data sources such as DNS responses that are not adequately sanitized before being incorporated into system output streams.
Mitigation strategies for this vulnerability include disabling reverse DNS lookups in the Apache configuration when they are not strictly necessary for operational requirements, implementing proper input sanitization for DNS resolution responses, and ensuring that log files are properly escaped and validated before being processed or displayed. Organizations should also consider implementing log monitoring systems that can detect anomalous patterns in log entries that might indicate injection attempts, and regularly review their Apache server configurations to ensure that DNS resolution is appropriately secured. Additionally, upgrading to newer versions of Apache HTTP Server that have addressed this specific vulnerability through improved input validation and sanitization mechanisms represents the most effective long-term solution to prevent exploitation of this class of attack.