CVE-2009-0093 in Windows
Summary
by MITRE
Windows DNS Server in Microsoft Windows 2000 SP4, Server 2003 SP1 and SP2, and Server 2008, when dynamic updates are enabled, does not restrict registration of the "wpad" hostname, which allows remote authenticated users to hijack the Web Proxy Auto-Discovery (WPAD) feature, and conduct man-in-the-middle attacks by spoofing a proxy server, via a Dynamic Update request for this hostname, aka "DNS Server Vulnerability in WPAD Registration Vulnerability," a related issue to CVE-2007-1692.
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Analysis
by VulDB Data Team • 08/30/2019
The vulnerability described in CVE-2009-0093 represents a critical security flaw in Microsoft Windows DNS Server implementations that affects multiple versions including Windows 2000 SP4, Server 2003 SP1 and SP2, and Server 2008. This vulnerability specifically targets the dynamic DNS update functionality and exploits a design oversight in hostname registration restrictions. The flaw enables authenticated remote attackers to register the well-known hostname "wpad" which is commonly used by Windows systems to automatically discover proxy server configurations through the Web Proxy Auto-Discovery protocol. This represents a significant weakness in the DNS server's access control mechanisms, as it fails to properly validate or restrict the registration of critical system hostnames that are part of standard Windows networking protocols. The vulnerability is particularly concerning because it directly impacts the trust model of Windows network environments and provides attackers with a mechanism to manipulate network traffic routing.
The technical implementation of this vulnerability stems from the Windows DNS Server's failure to enforce proper hostname validation during dynamic update requests. When dynamic updates are enabled, the DNS server accepts update requests without adequately checking whether the requested hostname conflicts with well-known system hostnames used by Windows networking protocols. The wpad hostname serves a specific purpose in Windows environments where systems automatically query DNS for a proxy configuration file to facilitate internet connectivity. By allowing unauthorized registration of this hostname, the DNS server effectively enables attackers to insert themselves into the network's proxy discovery process. This creates a man-in-the-middle attack vector where malicious actors can respond to wpad requests and redirect network traffic through their own proxy servers, potentially intercepting sensitive data or injecting malicious content. The vulnerability operates at the DNS protocol level and leverages the legitimate dynamic update functionality that administrators typically enable for network management purposes.
The operational impact of this vulnerability extends beyond simple network disruption to encompass serious data security implications. When an attacker successfully registers the wpad hostname, they can effectively hijack the proxy auto-discovery mechanism that Windows clients rely upon for internet connectivity. This allows them to redirect traffic through their own systems, enabling various attack vectors including credential theft, data interception, and malware distribution. Network administrators who have dynamic DNS updates enabled are particularly at risk since the vulnerability requires only authenticated access to perform the malicious update request. The attack scenario becomes more dangerous when considering that many organizations have dynamic updates enabled as part of their standard network management practices. This vulnerability directly relates to CWE-264, which addresses permissions, privileges, and access control issues, and aligns with ATT&CK technique T1187 for DNS tunneling and T1566 for credential harvesting through man-in-the-middle attacks.
Organizations affected by this vulnerability should implement immediate mitigations focusing on DNS server configuration and access control restrictions. The primary recommendation involves disabling dynamic updates on DNS servers when they are not required for network operations, particularly in environments where the risk of unauthorized access is high. Network segmentation and access control lists should be implemented to restrict which systems can perform dynamic DNS updates, ensuring that only authorized administrative systems can modify DNS records. Additionally, administrators should consider implementing DNS zone transfer restrictions and monitoring for unusual DNS update patterns that might indicate unauthorized hostname registrations. The vulnerability demonstrates the importance of proper input validation and hostname restriction mechanisms in DNS server implementations, aligning with security best practices outlined in NIST SP 800-128 for DNS security. Organizations should also consider implementing network monitoring solutions that can detect and alert on suspicious DNS update activities, particularly around well-known system hostnames. Regular security assessments and penetration testing should include validation of DNS server configurations to ensure that similar vulnerabilities are not present in other system components that might provide similar attack vectors through dynamic update functionality.