CVE-2004-0892 in Proxy Server
Summary
by MITRE
Microsoft Proxy Server 2.0 and Microsoft ISA Server 2000 (which is included in Small Business Server 2000 and Small Business Server 2003 Premium Edition) allows remote attackers to spoof trusted Internet content on a specially crafted webpage via spoofed reverse DNS lookup results.
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Analysis
by VulDB Data Team • 07/07/2025
This vulnerability resides in the domain name resolution mechanisms of Microsoft Proxy Server 2.0 and Microsoft ISA Server 2000, which are critical components in enterprise network security infrastructure. The flaw specifically exploits the trust relationship between DNS resolution and content validation, allowing remote attackers to manipulate the system's ability to verify the authenticity of internet content. When a user accesses a webpage through these proxy servers, the system performs reverse DNS lookups to validate the source of content, but this process can be manipulated through forged DNS responses. The vulnerability is classified under CWE-200, which deals with information exposure, and represents a significant weakness in the trust model that these servers rely upon for content validation. This issue particularly affects organizations using Small Business Server 2000 and Small Business Server 2003 Premium Edition, where these proxy components are integrated into the core infrastructure.
The technical implementation of this vulnerability leverages the inherent weaknesses in the reverse DNS lookup process used by these proxy servers for content authentication. When a client requests content through the proxy, the server performs a reverse DNS lookup to verify that the content originates from a trusted source, but attackers can manipulate DNS resolution results to make the proxy believe that malicious content is coming from a legitimate source. This spoofing technique exploits the trust relationship between the DNS resolution process and the content validation mechanism, allowing attackers to present forged content as if it were from a trusted domain. The attack vector operates at the network layer, where DNS responses are not properly validated or authenticated before being accepted by the proxy server. This vulnerability directly relates to the ATT&CK technique T1071.004, which covers application layer protocol: DNS, and demonstrates how DNS-based attacks can be used to bypass security controls. The flaw essentially allows an attacker to perform a man-in-the-middle attack by manipulating the DNS resolution process that the proxy server uses to validate content sources.
The operational impact of this vulnerability extends beyond simple content spoofing to potentially enable more sophisticated attacks within the compromised network environment. Organizations using these proxy servers become vulnerable to various malicious activities including phishing attacks, credential theft, and unauthorized access to internal resources. The vulnerability allows attackers to make users believe they are accessing legitimate websites while actually being served malicious content, which can lead to complete compromise of user sessions and sensitive data exposure. Network administrators face significant challenges in detecting such attacks since they appear to originate from trusted sources within the DNS infrastructure. The risk is particularly high in small business environments where these servers are commonly deployed, as these organizations often lack the sophisticated monitoring and security measures found in larger enterprises. This vulnerability can also be leveraged as a stepping stone for further attacks, potentially allowing attackers to establish persistence within the network or escalate privileges through the manipulation of trusted content delivery.
Mitigation strategies for this vulnerability must address both the immediate security gap and the underlying DNS trust mechanisms. Organizations should implement DNS security measures including DNSSEC validation to prevent spoofed DNS responses from being accepted by the proxy servers. Network segmentation and additional monitoring controls should be deployed to detect anomalous DNS resolution patterns that might indicate an attack attempt. The most effective long-term solution involves upgrading to newer versions of proxy server software that have addressed these DNS validation weaknesses and implemented more robust authentication mechanisms. Security patches released by Microsoft for this vulnerability should be applied immediately, and organizations should consider implementing additional security controls such as web application firewalls and content filtering solutions. The remediation process should include comprehensive network monitoring to detect and prevent DNS spoofing attempts, as well as regular security assessments to ensure that DNS resolution processes are properly validated before being accepted by proxy servers. Organizations should also implement proper network access controls and consider using alternative DNS resolution mechanisms that provide stronger authentication guarantees than the vulnerable reverse DNS lookup processes.