IIS extended unicode directory traversal vulnerability
Description
This vulnerability affects Microsoft IIS web servers that fail to properly validate URL-encoded Unicode characters in file path requests. Attackers can exploit this flaw by using extended Unicode representations (such as %c0%af or %c1%9c) as substitutes for standard directory traversal characters like forward slash (/) and backslash (\). This allows bypassing of path validation filters and enables unauthorized access to files outside the intended web root directory.
Remediation
Apply the appropriate security patches from Microsoft immediately:
1. For IIS 4.0: Install Windows NT 4.0 Security Rollup Package or later
2. For IIS 5.0: Install Windows 2000 Security Patch MS00-078 or later
3. Verify patches are applied by testing with known exploit patterns
4. Review and restrict IUSR account permissions to minimum required access
5. Implement additional security measures such as URL filtering and input validation at the application level
6. Consider upgrading to a currently supported version of IIS, as IIS 4.0 and 5.0 are no longer maintained
7. Monitor web server logs for suspicious Unicode-encoded requests indicating exploitation attempts