CVE-2001-0709 in IIS
Summary
by MITRE
Microsoft IIS 4.0 and before, when installed on a FAT partition, allows a remote attacker to obtain source code of ASP files via a URL encoded with Unicode.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/11/2017
This vulnerability exists in Microsoft Internet Information Services versions 4.0 and earlier when installed on FAT file systems, representing a critical security flaw that enables remote code disclosure. The issue stems from how IIS handles URL decoding processes on FAT partitions, where Unicode encoded URLs can be manipulated to access ASP source code files. The vulnerability specifically exploits the interaction between the web server's file system handling and its URL parsing mechanisms, creating an information disclosure channel that could expose sensitive application source code to unauthorized users.
The technical root cause involves the improper handling of Unicode URL encoding within the IIS web server when operating on FAT file systems. When a malicious user crafts a specially encoded URL containing Unicode characters, the server fails to properly validate or sanitize the input before processing file requests. This allows attackers to traverse directory structures and access ASP source files that should remain protected. The vulnerability is specifically tied to FAT partition limitations in how file names and paths are processed, making it a filesystem-specific weakness rather than a general protocol flaw. This aligns with CWE-20, which addresses improper input validation, and CWE-312, concerning exposure of sensitive data through information leakage.
The operational impact of this vulnerability is severe as it provides attackers with complete access to application source code, including embedded database connection strings, business logic, and potentially sensitive configuration details. This exposure can lead to further exploitation opportunities such as discovering additional vulnerabilities in the application code, understanding the application architecture, or identifying potential attack vectors. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can be automated, allowing for rapid reconnaissance of multiple web applications. Attackers can leverage this information to conduct more sophisticated attacks including injection attacks, privilege escalation, or social engineering campaigns based on discovered code patterns.
Mitigation strategies for this vulnerability include immediate patching of affected IIS versions, which was addressed in subsequent releases through proper URL validation and sanitization. Organizations should also implement proper file system permissions and avoid installing IIS on FAT partitions when possible, as the vulnerability is specifically tied to FAT filesystem behavior. Network-level protections such as web application firewalls can help detect and block suspicious URL encoding patterns, while monitoring systems should be configured to alert on unusual file access patterns or attempts to access ASP source files. Additionally, implementing secure coding practices and regular security assessments can help identify similar vulnerabilities in other web applications. The vulnerability demonstrates the importance of proper input validation and the potential security implications of filesystem-specific implementation choices, aligning with ATT&CK technique T1566 for credential access through exploitation of web application vulnerabilities and T1083 for file and directory discovery.