CVE-2000-0630 in IIS
Summary
by MITRE
IIS 4.0 and 5.0 allows remote attackers to obtain fragments of source code by appending a +.htr to the URL, a variant of the "File Fragment Reading via .HTR" vulnerability.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/13/2025
The vulnerability described in CVE-2000-0630 represents a critical information disclosure flaw affecting Microsoft Internet Information Services versions 4.0 and 5.0. This vulnerability stems from improper handling of file requests containing specific extensions that trigger unexpected behavior in the web server's processing pipeline. The issue specifically manifests when attackers append a +.htr suffix to targeted URLs, enabling them to access fragments of source code from files that should remain protected. This vulnerability falls under the broader category of information disclosure vulnerabilities and is classified as CWE-200, which encompasses weaknesses that result in information exposure. The flaw exploits the web server's interpretation of file extensions and directory traversal mechanisms, creating an unintended access path that bypasses normal security controls.
The technical implementation of this vulnerability occurs within the IIS web server's request processing logic where it fails to properly validate or sanitize file extension parameters. When a request is made with the +.htr suffix, the server's internal file resolution mechanism attempts to process the request in a manner that exposes internal file contents, particularly source code fragments from server-side includes and other dynamic content. This behavior is particularly dangerous because it allows attackers to extract sensitive information from server files without proper authentication or authorization. The vulnerability operates at the application layer and can be classified under the ATT&CK technique T1566.001 for initial access through spearphishing attachments, though in this case the attack vector is more directly related to web server misconfiguration and improper input validation.
The operational impact of this vulnerability extends beyond simple information disclosure, as the extracted source code fragments may contain sensitive elements such as database connection strings, API keys, application logic, and other confidential information that could be leveraged for further exploitation. Attackers can systematically probe different URLs with the +.htr suffix to gather progressively more information about the target system's internal structure and implementation details. This vulnerability affects the confidentiality aspect of the CIA triad and can lead to cascading security issues if the leaked information includes authentication mechanisms, file paths, or application logic that could be used to craft more sophisticated attacks. The vulnerability is particularly concerning in environments where IIS 4.0 and 5.0 are still operational, as these older versions lack modern security features and regular updates.
Mitigation strategies for this vulnerability require immediate implementation of server configuration changes and software updates to address the root cause. Organizations should ensure that all IIS servers are updated to supported versions that have patched this vulnerability, as both IIS 4.0 and 5.0 reached end-of-life and no longer receive security updates from Microsoft. The recommended approach includes implementing proper input validation and sanitization for all file extension requests, configuring the web server to reject or properly handle requests with unusual or potentially malicious file extensions, and applying security patches that address the specific handling of .htr files and related extensions. Network segmentation and access controls should be implemented to limit exposure of vulnerable systems, while security monitoring should be enhanced to detect and alert on suspicious requests containing the +.htr suffix pattern. Additionally, regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in web server configurations and application code that may present analogous attack vectors.