CVE-2002-0440 in Interscan Viruswall
Summary
by MITRE
Trend Micro InterScan VirusWall HTTP proxy 3.6 with the "Skip scanning if Content-length equals 0" option enabled allows malicious web servers to bypass content scanning via a Content-length header set to 0, which is often ignored by HTTP clients.
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Analysis
by VulDB Data Team • 12/29/2024
The vulnerability identified as CVE-2002-0440 affects Trend Micro InterScan VirusWall version 3.6 when configured with the specific "Skip scanning if Content-length equals 0" option. This security flaw represents a critical bypass mechanism that undermines the fundamental purpose of web proxy content scanning. The vulnerability operates at the HTTP protocol level where the proxy server fails to properly validate content length headers, creating an exploitable condition that malicious actors can leverage to evade detection. This issue directly impacts the integrity of the security posture by allowing potentially harmful content to pass through the inspection process without proper analysis.
The technical implementation of this vulnerability stems from the proxy server's improper handling of HTTP Content-Length headers during the scanning process. When the Content-Length header is set to zero, legitimate HTTP clients typically ignore such headers or treat them as invalid, but the InterScan VirusWall proxy fails to properly validate this condition. The flaw occurs because the system assumes that content with zero length is either empty or irrelevant, thus skipping the scanning process entirely. This behavior creates a security gap where attackers can craft HTTP responses with Content-Length: 0 headers that bypass the antivirus scanning mechanism, effectively allowing malicious content to traverse the proxy undetected. The vulnerability demonstrates a classic case of insufficient input validation and improper security decision making based on malformed HTTP headers.
The operational impact of this vulnerability extends beyond simple content bypass to represent a significant threat to organizational security infrastructure. When exploited, this vulnerability allows attackers to deliver malicious content through web servers that would normally be inspected by the proxy, potentially leading to malware distribution, data exfiltration, or other malicious activities. The bypass affects the core functionality of the antivirus proxy by creating a condition where the system's decision-making process fails to properly evaluate content based on its actual characteristics rather than potentially misleading header information. Organizations relying on this proxy configuration face the risk of undetected malicious traffic passing through their network perimeter, undermining the effectiveness of their security controls and potentially exposing sensitive systems to compromise.
This vulnerability aligns with CWE-20, which addresses "Improper Input Validation," and demonstrates how insufficient validation of HTTP headers can lead to security bypass scenarios. The flaw also relates to ATT&CK technique T1071.004, which covers "Application Layer Protocol: DNS" but more broadly represents protocol manipulation techniques that bypass security controls. Organizations should implement immediate mitigations including disabling the problematic configuration option, implementing additional validation checks on Content-Length headers, and ensuring that all HTTP responses are properly scanned regardless of header values. The vulnerability highlights the importance of proper HTTP protocol implementation and the necessity of validating all input parameters, including headers, to prevent such bypass conditions. Additionally, network administrators should consider implementing additional security measures such as deep packet inspection and behavioral analysis to detect anomalous HTTP traffic patterns that may indicate exploitation attempts.