CVE-2001-0333 in IIS
Summary
by MITRE
Directory traversal vulnerability in IIS 5.0 and earlier allows remote attackers to execute arbitrary commands by encoding .. (dot dot) and "\" characters twice.
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Analysis
by VulDB Data Team • 10/07/2025
The vulnerability identified as CVE-2001-0333 represents a critical directory traversal flaw in Microsoft Internet Information Services version 5.0 and earlier systems. This weakness stems from insufficient input validation mechanisms within the web server's handling of URL-encoded path sequences, specifically targeting the double encoding of directory traversal sequences. The vulnerability exploits a fundamental flaw in how IIS processes requests containing encoded .. (dot dot) sequences combined with backslash characters, allowing unauthorized access to files and directories outside the intended web root.
The technical implementation of this vulnerability occurs at the application layer where IIS fails to properly decode and validate URL-encoded sequences before processing file system requests. When an attacker submits a request containing double-encoded directory traversal sequences such as ..%255C..%255C (where %255C represents a backslash character), the web server incorrectly interprets these sequences, leading to path resolution that bypasses normal security boundaries. This flaw operates at the HTTP protocol level and affects the core file system access mechanisms within IIS, making it particularly dangerous as it can be exploited through standard web browser interactions without requiring special privileges or tools.
The operational impact of CVE-2001-0333 extends beyond simple file access violations to encompass complete system compromise potential. Attackers can leverage this vulnerability to execute arbitrary commands on the affected server by accessing system files, configuration data, and potentially gaining access to sensitive information stored on the web server. The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and represents a classic example of path traversal attacks that have been consistently documented in security literature. This flaw particularly affects systems running IIS 5.0 or earlier versions where the security mechanisms for validating file system paths were inadequate to prevent such exploitation scenarios.
Organizations affected by this vulnerability face significant risks including data breaches, system compromise, and potential regulatory violations. The attack vector is particularly concerning because it can be executed through standard web browsing activities, making detection difficult and potentially allowing attackers to remain undetected for extended periods. Mitigation strategies include implementing proper input validation, applying Microsoft security patches, configuring IIS to disable unnecessary features, and deploying web application firewalls to filter suspicious URL patterns. The vulnerability also maps to ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation would enable attackers to execute arbitrary commands on the compromised system. Organizations should prioritize immediate patching of affected systems and implement comprehensive monitoring to detect potential exploitation attempts, as this vulnerability has been widely documented and exploited in various attack campaigns throughout the early 2000s.