CVE-2003-0042 in Tomcat
Summary
by MITRE
Jakarta Tomcat before 3.3.1a, when used with JDK 1.3.1 or earlier, allows remote attackers to list directories even with an index.html or other file present, or obtain unprocessed source code for a JSP file, via a URL containing a null character.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability described in CVE-2003-0042 represents a critical directory traversal and information disclosure flaw affecting Apache Jakarta Tomcat versions prior to 3.3.1a when operating with JDK 1.3.1 or earlier versions. This security weakness stems from improper handling of null characters within URL requests, creating a pathway for malicious actors to bypass access controls and gain unauthorized visibility into server directories. The flaw specifically exploits how Tomcat processes incoming requests containing null characters, allowing attackers to manipulate the request parsing mechanism and access resources that should otherwise remain protected.
The technical implementation of this vulnerability occurs at the application level where Tomcat's request processing logic fails to properly sanitize or validate null characters embedded within URLs. When a null character is present in a request URL, the servlet container's parsing mechanism becomes confused, potentially causing it to interpret the request differently than intended. This misinterpretation enables attackers to traverse directory structures that should be restricted, as well as access JSP source code files in their unprocessed form rather than executing them through the server's Java runtime environment. The vulnerability is particularly dangerous because it operates at the HTTP request level, making it difficult to detect through standard network monitoring tools.
The operational impact of this vulnerability extends beyond simple directory listing capabilities to include potential exposure of sensitive source code and application logic. When attackers can access unprocessed JSP files, they gain visibility into server-side code implementations, which may contain database connection strings, business logic, or other sensitive information that could be exploited in subsequent attacks. The ability to list directories even when index files are present undermines fundamental web application security principles and allows for reconnaissance activities that could lead to more sophisticated attacks. This vulnerability particularly affects older systems running legacy Java versions where security patches and updates may not have been applied, creating a significant risk for organizations maintaining outdated web infrastructure.
Organizations should prioritize immediate remediation by upgrading to Tomcat 3.3.1a or later versions that properly address null character handling in URL requests. System administrators must also ensure that all Java runtime environments are updated to supported versions, as JDK 1.3.1 and earlier contain known security vulnerabilities that compound the risks associated with this flaw. Network security controls should include monitoring for unusual URL patterns containing null characters, though such detection may prove challenging given the nature of the attack vector. The vulnerability aligns with CWE-22 Directory Traversal and CWE-502 Deserialization of Untrusted Data categories, representing a classic case of improper input validation. From an ATT&CK framework perspective, this vulnerability maps to T1083 File and Directory Discovery and T1213 Data from Information Repositories techniques, as attackers can use it to enumerate system resources and extract sensitive information. Additionally, the vulnerability demonstrates the importance of proper input sanitization and the potential consequences of legacy software support gaps in enterprise security infrastructure.