CVE-2002-2234 in ScreenOS
Summary
by MITRE
NetScreen ScreenOS before 4.0.1 allows remote attackers to bypass the Malicious-URL blocking feature by splitting the URL into fragmented IP requests.
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Analysis
by VulDB Data Team • 03/27/2017
The vulnerability described in CVE-2002-2234 represents a significant security flaw in NetScreen ScreenOS firewall software versions prior to 4.0.1. This issue specifically targets the firewall's ability to prevent access to malicious web resources through its URL filtering mechanism. The vulnerability exploits a fundamental weakness in how the system processes and validates network traffic, particularly when dealing with fragmented internet protocol packets that contain URL information.
The technical flaw stems from the improper handling of IP fragmentation within the firewall's malicious URL blocking feature. When attackers send URLs that exceed the maximum transmission unit size, the packets get fragmented during transmission. The vulnerable ScreenOS version fails to properly reassemble these fragmented packets before checking them against the malicious URL database, allowing attackers to bypass the security controls by splitting their malicious URLs across multiple IP fragments. This technique exploits a gap in the network protocol processing logic where the firewall validates the complete URL after reassembly rather than during the initial packet inspection phase.
The operational impact of this vulnerability is substantial as it effectively neutralizes one of the primary security controls designed to protect organizations from accessing known malicious websites. Attackers can leverage this flaw to deliver malware, phishing content, or other malicious resources without triggering the firewall's URL filtering mechanisms. This bypass capability undermines the entire security posture of organizations relying on NetScreen firewalls for web content filtering, potentially leading to data breaches, malware infections, and unauthorized access to corporate networks. The vulnerability is particularly dangerous because it operates at the network layer, making it difficult to detect through traditional application-level monitoring systems.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to ScreenOS version 4.0.1 or later, which contains the necessary fixes for proper IP fragment reassembly and URL validation. Network administrators should also consider implementing additional security controls such as deep packet inspection, web proxy solutions, or alternative URL filtering mechanisms that do not rely on the vulnerable ScreenOS functionality. The vulnerability aligns with CWE-129, which addresses improper validation of input, and reflects techniques commonly associated with attack patterns in the MITRE ATT&CK framework under the network denial of service and command and control categories. Organizations should conduct thorough security assessments to identify any potential exploitation attempts and ensure that all network security devices are running patched versions to prevent similar vulnerabilities from being exploited in the future.