CVE-2000-0649 in IIS
Summary
by MITRE
IIS 4.0 allows remote attackers to obtain the internal IP address of the server via an HTTP 1.0 request for a web page which is protected by basic authentication and has no realm defined.
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Analysis
by VulDB Data Team • 05/23/2025
This vulnerability exists in Microsoft Internet Information Services version 4.0 and represents a significant information disclosure flaw that can be exploited by remote attackers to discover internal network addresses. The vulnerability specifically affects servers configured with basic authentication without a defined realm parameter, creating an opportunity for attackers to gather sensitive network information through crafted HTTP requests. The flaw stems from the server's improper handling of authentication responses when no realm is specified, allowing the internal IP address to be exposed in the HTTP response headers.
The technical implementation of this vulnerability occurs when a remote attacker sends an HTTP 1.0 request to a web page protected by basic authentication but lacking a realm definition in the authentication challenge. The IIS 4.0 server responds to this specific scenario by including the internal IP address in the response, typically within the WWW-Authenticate header or other response metadata. This occurs because the server defaults to exposing internal addressing information when authentication parameters are incomplete or unspecified, creating a pathway for reconnaissance activities that could lead to more sophisticated attacks.
The operational impact of CVE-2000-0649 extends beyond simple information disclosure, as the exposure of internal IP addresses can facilitate subsequent attacks within the network infrastructure. Attackers can leverage this information to conduct network mapping, identify internal services, and potentially exploit other vulnerabilities that may be present on the internal network. This vulnerability aligns with CWE-200, which addresses information exposure, and demonstrates how seemingly minor configuration issues can create significant security risks. The flaw can be categorized under ATT&CK technique T1046, as it enables network service discovery through information gathering activities that can be automated and scaled.
Organizations affected by this vulnerability should implement immediate mitigations including proper configuration of basic authentication with defined realms, regular security updates to IIS 4.0 installations, and network segmentation to limit the impact of information disclosure. The recommended approach involves configuring authentication challenges with explicit realm definitions to prevent the server from defaulting to internal address exposure. Additionally, implementing proper network monitoring and intrusion detection systems can help identify exploitation attempts. This vulnerability highlights the importance of following security best practices for authentication configuration and demonstrates how legacy systems can contain fundamental flaws that persist across multiple versions. Organizations should consider migrating away from unsupported IIS 4.0 versions and implement comprehensive security policies that require explicit authentication parameters to prevent similar issues in modern deployments.