CVE-1999-0154

Step 1: Target Identification: The attacker identifies a web server running IIS 2.0 or 3.0. Step 2: URL Crafting: The attacker crafts a URL targeting an ASP file, appending a period (.) to the end of the filename (e.g., http://example.com/vulnerable.asp.). Step 3: Request Submission: The attacker sends the crafted URL request to the vulnerable IIS server. Step 4: Source Code Disclosure: The IIS server, due to the vulnerability, fails to interpret the ASP file and instead returns the raw source code of the ASP file to the attacker.

The vulnerability stems from a flaw in how IIS handles file extensions and URL parsing. Specifically, the web server fails to properly sanitize the input when a period (.) is appended to the end of a URL requesting an ASP file. This causes the server to bypass the ASP interpreter and instead return the raw source code of the ASP file. The root cause is likely a missing or inadequate check in the file processing logic, failing to recognize and block the appended period, thereby exposing the file's contents directly. This is a classic example of a path traversal vulnerability, where an attacker can manipulate the URL to bypass intended security controls.