CVE-2008-3494 in R3000 Internet Filter
Summary
by MITRE
8e6 R3000 Internet Filter 2.0.12.10 allows remote attackers to bypass intended restrictions via an extra HTTP Host header with additional leading text placed before the real Host header.
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Analysis
by VulDB Data Team • 01/25/2025
The CVE-2008-3494 vulnerability affects the 8e6 R3000 Internet Filter version 2.0.12.10, a network security appliance designed to enforce web content filtering policies. This device operates as a proxy server that intercepts and analyzes HTTP traffic to enforce access control restrictions based on domain names and other criteria. The vulnerability stems from improper handling of HTTP headers during the filtering process, specifically in how the system processes the Host header field that is critical for determining the target website of HTTP requests. The flaw manifests when an attacker crafts a malicious HTTP request containing multiple Host headers, with the first header containing additional leading text that precedes the legitimate Host header, allowing the filter to bypass intended restrictions.
The technical implementation of this vulnerability exploits a common pattern in HTTP header processing where systems may only examine the first occurrence of a header field or fail to properly validate the structure of headers. In the context of web filtering appliances, the system typically relies on the Host header to determine which domain name should be subject to access control policies. When an attacker places additional text before the legitimate Host header, the filtering logic may interpret this malformed header incorrectly, causing the appliance to either ignore the intended restriction or misclassify the destination website. This behavior represents a classic case of input validation failure and improper header parsing, which falls under CWE-20 Input Validation and CWE-776 Improper Restriction of XML External Entity Reference. The vulnerability is particularly concerning because it directly undermines the core security function of the device by allowing unauthorized access to restricted websites.
The operational impact of this vulnerability extends beyond simple bypass of content restrictions, potentially exposing organizations to various security risks including access to malicious websites, data exfiltration, and compromise of sensitive information. Organizations relying on the 8e6 R3000 for network security enforcement may experience unauthorized access to blocked categories of websites, including those containing malware, phishing content, or inappropriate material. The vulnerability allows attackers to circumvent security controls without requiring authentication or specialized tools, making it particularly dangerous in enterprise environments where strict web access policies are enforced. According to ATT&CK framework, this vulnerability maps to T1071.001 Application Layer Protocol: Web Protocols and T1566 Credential Access, as it enables unauthorized access to web resources and potentially allows attackers to establish persistence through access to restricted domains. The attack surface is particularly broad since the vulnerability affects the fundamental HTTP processing capabilities of the appliance, potentially allowing attackers to access any restricted content category that the appliance was designed to block.
Mitigation strategies for this vulnerability require immediate attention from network administrators and security teams responsible for 8e6 R3000 deployments. The primary recommendation involves applying the vendor-provided security update or firmware patch that addresses the HTTP header parsing issue. Organizations should also implement network monitoring to detect unusual HTTP traffic patterns that may indicate exploitation attempts, including requests with malformed headers or unexpected Host header combinations. Network segmentation and additional layers of security controls should be considered as defensive measures to reduce the impact if the vulnerability is exploited. Security teams should conduct comprehensive vulnerability assessments of all similar filtering appliances in their environment and establish monitoring procedures for detecting malformed HTTP headers in network traffic logs. The vulnerability highlights the importance of robust input validation and proper header handling in security appliances, emphasizing the need for security-by-design principles in network filtering systems. Additionally, organizations should review their incident response procedures to ensure readiness for potential exploitation of this class of vulnerability, particularly in environments where web filtering is critical for compliance and security policy enforcement.