CVE-2000-0770 in IIS
Summary
by MITRE
IIS 4.0 and 5.0 does not properly restrict access to certain types of files when their parent folders have less restrictive permissions, which could allow remote attackers to bypass access restrictions to some files, aka the "File Permission Canonicalization" vulnerability.
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Analysis
by VulDB Data Team • 10/12/2025
The CVE-2000-0770 vulnerability represents a critical access control flaw in Microsoft Internet Information Services versions 4.0 and 5.0 that exploits file permission canonicalization issues. This vulnerability stems from how IIS handles path resolution when processing requests for files located within directories that have more permissive access controls than the files themselves. The flaw occurs during the canonicalization process where IIS fails to properly validate and enforce access restrictions when resolving file paths that traverse through parent directories with less restrictive permissions. This creates a scenario where attackers can bypass intended access controls and gain unauthorized access to protected files that should be restricted based on their directory permissions.
The technical implementation of this vulnerability leverages the way IIS processes URL paths and resolves file locations within the file system. When a request is made for a specific file that exists within a directory structure where parent directories have broader access permissions, the canonicalization process in IIS does not properly enforce the restrictive permissions of the target file's actual directory. This allows attackers to craft URLs that appear to target restricted files but are actually resolved through paths that bypass the intended access controls. The vulnerability specifically affects the path resolution logic in IIS web server implementations and is categorized under CWE-22, which addresses improper limitation of a pathname to a restricted directory. This weakness enables path traversal attacks by allowing the web server to resolve paths in ways that do not properly enforce the security boundaries established by directory permissions.
The operational impact of CVE-2000-0770 is significant as it can enable remote attackers to access sensitive files and data that should be protected by directory-level access controls. Attackers can exploit this vulnerability to read configuration files, source code, database files, and other sensitive information that may contain credentials, business logic, or other confidential data. The vulnerability can be particularly dangerous in environments where IIS servers host multiple applications with varying security requirements, as it allows attackers to move laterally through the file system and potentially access files across different application boundaries. This type of vulnerability directly impacts the principle of least privilege and can lead to complete system compromise if attackers can access critical system files or administrative configuration data.
The attack surface for this vulnerability extends beyond simple file access and can be leveraged as part of broader exploitation campaigns. According to ATT&CK framework, this vulnerability aligns with techniques involving privilege escalation and credential access through path traversal methods. Security professionals should consider implementing multiple layers of defense including web application firewalls, proper directory permission configurations, and regular security audits of IIS server configurations. Organizations should also ensure that all IIS servers are updated to supported versions and that proper access control lists are implemented at both directory and file levels. The vulnerability highlights the importance of proper input validation and path resolution within web server implementations, emphasizing the need for robust canonicalization processes that maintain security boundaries throughout the file system traversal process. Mitigation strategies should include disabling unnecessary features, implementing strict access controls, and conducting regular penetration testing to identify similar path traversal vulnerabilities in web server configurations.