CVE-1999-0154 in IIS
Summary
by MITRE
IIS 2.0 and 3.0 allows remote attackers to read the source code for ASP pages by appending a . (dot) to the end of the URL.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/26/2025
This vulnerability exists in Microsoft Internet Information Services versions 2.0 and 3.0 where the web server fails to properly validate file extensions in URL requests. When a user appends a period or dot character to the end of an ASP page URL, the server incorrectly processes the request and returns the raw source code of the ASP file instead of executing it. This occurs due to insufficient input sanitization and improper handling of malformed URLs that contain trailing dots. The flaw stems from the server's inability to distinguish between legitimate file requests and malicious attempts to bypass execution boundaries. The vulnerability is categorized under CWE-20 as improper input validation, specifically failing to properly handle file path requests. This represents a critical security flaw that directly violates the principle of least privilege and allows unauthorized access to sensitive server-side code. The vulnerability is particularly dangerous because ASP source code often contains database connection strings, authentication credentials, and business logic that could be exploited by attackers. According to ATT&CK framework, this maps to T1566.001 for initial access through malicious files and T1083 for discovery of files and directories. The impact extends beyond simple information disclosure as the leaked source code can reveal implementation details that aid in developing more sophisticated attacks against the application. Attackers can leverage this vulnerability to understand application architecture, identify hardcoded secrets, and discover potential injection points within the code. The flaw affects the confidentiality and integrity aspects of the CIA triad by exposing sensitive information and potentially enabling further exploitation. This vulnerability is particularly concerning in environments where IIS 2.0 and 3.0 are still operational, as these older versions lack modern security protections. The attack vector is simple and requires minimal technical skill, making it accessible to attackers with basic knowledge of web application exploitation. Organizations should immediately implement proper URL validation mechanisms and ensure that all web servers properly sanitize input parameters. The recommended mitigation includes applying security patches, configuring proper directory permissions, and implementing web application firewalls that can detect and block such malformed requests. Additionally, regular security assessments should be conducted to identify and remediate similar vulnerabilities in legacy systems. The vulnerability demonstrates the importance of input validation and proper request handling in web server implementations, as well as the necessity of keeping systems updated with the latest security patches.