CVE-2003-0866 in Tomcat
Summary
by MITRE
The Catalina org.apache.catalina.connector.http package in Tomcat 4.0.x up to 4.0.3 allows remote attackers to cause a denial of service via several requests that do not follow the HTTP protocol, which causes Tomcat to reject later requests.
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Analysis
by VulDB Data Team • 07/20/2025
The vulnerability described in CVE-2003-0866 represents a significant denial of service weakness within the Apache Tomcat 4.0.x web server software family. This flaw specifically affects the catalina connector http package implementation and demonstrates how improper handling of malformed HTTP requests can lead to system instability and service disruption. The vulnerability exists in Tomcat versions 4.0.0 through 4.0.3, making it a critical issue for organizations running these older versions of the popular Java application server. The security implications extend beyond simple service interruption as this weakness can be exploited by remote attackers without requiring authentication or privileged access, making it particularly dangerous in production environments.
The technical nature of this vulnerability stems from the way Tomcat processes HTTP requests that deviate from standard protocol specifications. When the http connector receives malformed requests that do not properly adhere to HTTP protocol requirements, the server's request parsing mechanism becomes overwhelmed or enters an inconsistent state. This improper handling causes the server to reject subsequent legitimate requests, effectively creating a denial of service condition where authorized users cannot access the web application services. The flaw demonstrates inadequate input validation and error handling within the connector component, allowing malformed data to cascade into system-wide service degradation rather than being properly rejected or handled gracefully.
From an operational perspective, this vulnerability creates substantial risk for web applications hosted on affected Tomcat versions. Attackers can exploit this weakness by sending carefully crafted malformed HTTP requests that trigger the denial of service condition, potentially causing significant business disruption and service unavailability. The impact extends beyond immediate service interruption as organizations may experience extended downtime while administrators work to restore service and implement fixes. Network administrators and security teams must also contend with the fact that this attack can be executed remotely without requiring any special privileges or access credentials, making it an attractive vector for malicious actors seeking to disrupt web services. The vulnerability essentially allows attackers to consume server resources and processing capacity in a way that renders legitimate service requests impossible to process.
Organizations affected by this vulnerability should prioritize immediate remediation through patching or upgrading to newer Tomcat versions that contain fixes for this specific issue. The recommended mitigation strategy involves upgrading to Tomcat 4.0.4 or later versions where this denial of service vulnerability has been addressed through improved input validation and error handling mechanisms. Additionally, implementing network-level protections such as intrusion detection systems and rate limiting can help reduce the impact of such attacks by identifying and blocking malformed request patterns. Security practitioners should also consider deploying web application firewalls that can detect and filter abnormal HTTP traffic patterns that may indicate exploitation attempts. This vulnerability highlights the importance of proper input validation and robust error handling in web server implementations, as outlined in CWE-20 for improper input validation and CWE-400 for unspecified denial of service conditions. The attack vector aligns with ATT&CK technique T1499.004 for network denial of service, demonstrating how protocol-level weaknesses can be exploited to compromise availability. Organizations should also implement comprehensive monitoring and logging to detect unusual request patterns that may indicate exploitation attempts, ensuring that security teams can respond quickly to potential attacks targeting this specific vulnerability.