CVE-2000-0149 in Zeus Web Server
Summary
by MITRE
Zeus web server allows remote attackers to view the source code for CGI programs via a null character (%00) at the end of a URL.
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Analysis
by VulDB Data Team • 10/19/2025
The vulnerability described in CVE-2000-0149 affects the Zeus web server implementation and represents a classic case of input validation failure that can lead to information disclosure. This weakness stems from the server's improper handling of null characters within URL parameters, creating a pathway for malicious actors to access sensitive source code files. The vulnerability specifically manifests when a null character %00 is appended to a URL, allowing remote attackers to bypass normal access controls and retrieve the underlying source code of CGI programs. This type of flaw falls under the category of improper input validation as defined by CWE-20, which addresses weaknesses related to insufficient validation of input data. The Zeus web server's failure to properly sanitize URL parameters creates an exploitable condition that directly violates the principle of least privilege and secure input handling.
The technical exploitation of this vulnerability relies on the web server's treatment of null-terminated strings and its handling of malformed URL requests. When a null character is appended to a URL, the server may interpret this as a legitimate request parameter while simultaneously failing to properly validate or sanitize the input. This creates a scenario where the server processes the request through its normal CGI execution pipeline but inadvertently exposes the source code of the program being executed. The vulnerability demonstrates a lack of proper boundary checking and input sanitization, which are fundamental security controls that should prevent such information leakage. From an ATT&CK perspective, this vulnerability maps to technique T1566.001 for initial access through malicious web content and T1083 for file and directory discovery, as attackers can enumerate and extract source code files that may contain sensitive information. The exploitation mechanism leverages the server's failure to properly handle null-terminated strings, which is a well-documented weakness in many legacy web server implementations.
The operational impact of this vulnerability extends beyond simple information disclosure, as source code exposure can provide attackers with detailed insights into application logic, database connection strings, and potential security flaws within the software. When CGI programs are exposed, attackers can analyze the code structure to identify additional vulnerabilities such as SQL injection points, buffer overflow opportunities, or insecure coding practices that may exist within the application. The exposure of source code represents a significant risk to system security as it eliminates the attacker's need to perform reconnaissance through other means, providing them with direct access to implementation details that would normally require extensive reverse engineering or exploitation attempts. This vulnerability can also facilitate further attacks, as the source code may contain hardcoded credentials, API keys, or other sensitive information that can be leveraged for privilege escalation or lateral movement within the network. The impact is particularly severe in environments where multiple applications are hosted on the same server, as the exposure of one application's source code can potentially reveal information about other applications running on the same platform.
Mitigation strategies for CVE-2000-0149 should focus on implementing proper input validation and sanitization mechanisms within the web server configuration. Organizations should ensure that their web server implementations properly handle null characters and other special characters in URL parameters by implementing strict input filtering and validation. The most effective immediate fix involves configuring the web server to reject or sanitize URLs containing null characters before they are processed by the CGI execution engine. This aligns with the defensive programming principles outlined in CWE-170, which addresses issues related to improper handling of null-terminated strings. Additionally, implementing proper access controls and authentication mechanisms can limit the impact of such vulnerabilities by ensuring that even if source code is exposed, unauthorized users cannot access sensitive functionality. Regular security updates and patches should be applied to web server software, as this vulnerability represents a known weakness that has been addressed in subsequent versions of most web server implementations. Network segmentation and monitoring solutions should also be deployed to detect and alert on unusual URL patterns or attempts to access source code files, providing an additional layer of defense against exploitation attempts.