CVE-2009-1122 in IIS
Summary
by MITRE
The WebDAV extension in Microsoft Internet Information Services (IIS) 5.0 on Windows 2000 SP4 does not properly decode URLs, which allows remote attackers to bypass authentication, and possibly read or create files, via a crafted HTTP request, aka "IIS 5.0 WebDAV Authentication Bypass Vulnerability," a different vulnerability than CVE-2009-1535.
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Analysis
by VulDB Data Team • 11/09/2025
The vulnerability identified as CVE-2009-1122 represents a critical authentication bypass flaw within Microsoft Internet Information Services version 5.0 running on Windows 2000 Service Pack 4 systems. This issue specifically affects the WebDAV extension component that enables remote file management capabilities through HTTP protocols. The vulnerability stems from improper URL decoding mechanisms within the IIS 5.0 WebDAV implementation, creating a pathway for malicious actors to circumvent the authentication controls that should normally protect sensitive resources and operations.
The technical flaw manifests when the WebDAV extension processes HTTP requests containing specially crafted URL-encoded sequences that are not properly decoded before authentication checks are performed. This improper handling allows attackers to manipulate the request processing flow in such a way that the authentication system fails to properly validate user credentials or access controls. The vulnerability specifically impacts the authentication mechanism during WebDAV operations, where the system's URL decoding routine does not adequately process encoded characters, leading to authentication bypass conditions that can be exploited by remote attackers without requiring valid credentials.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable full unauthorized access to the web server's file system. Attackers can leverage this flaw to read sensitive files, create new files, modify existing content, and potentially escalate their privileges within the compromised system. The vulnerability affects systems where WebDAV functionality is enabled, which typically includes file sharing and collaborative environments where remote users need to manage web content. The authentication bypass capability means that an attacker can perform actions that should require proper authorization, including accessing restricted directories, uploading malicious content, or modifying server configurations through the WebDAV interface.
This vulnerability aligns with CWE-20, which describes improper input handling in software systems, specifically focusing on issues related to input validation and processing. The flaw represents a classic case of inadequate data sanitization where the URL decoding process fails to properly normalize input before security checks are applied. From an adversarial perspective, this vulnerability maps to several ATT&CK techniques including T1078 for valid accounts usage and T1566 for credential harvesting through exploitation of authentication bypass vulnerabilities. The attack surface is particularly concerning for organizations using legacy systems where patching may not be feasible, as this vulnerability affects systems that are no longer supported by Microsoft, making remediation more challenging.
Mitigation strategies for CVE-2009-1122 should prioritize immediate system hardening measures including disabling WebDAV functionality when not required, implementing network segmentation to limit access to affected servers, and applying available security patches if possible. Organizations should also consider implementing additional access controls such as IP address restrictions, enhanced monitoring of WebDAV traffic, and regular security audits of web server configurations. The vulnerability highlights the importance of proper input validation and URL decoding mechanisms in web server implementations, emphasizing the need for comprehensive security testing of all components that handle user-supplied data. Given the age of the affected systems and the lack of vendor support, organizations should consider migrating to supported platforms or implementing compensating controls to reduce the risk exposure from this and similar legacy vulnerabilities.