CVE-2002-0234 in Netscreen ScreenOS
Summary
by MITRE
NetScreen ScreenOS before 2.6.1 does not support a maximum number of concurrent sessions for a system, which allows an attacker on the trusted network to cause a denial of service (resource exhaustion) via a port scan to an external network, which consumes all available connections.
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Analysis
by VulDB Data Team • 09/21/2025
The vulnerability identified as CVE-2002-0234 affects NetScreen ScreenOS versions prior to 2.6.1 and represents a critical resource exhaustion flaw that can be exploited to achieve denial of service conditions. This vulnerability specifically targets the absence of session limiting mechanisms within the firewall's connection handling architecture, creating a scenario where an attacker can systematically consume all available system resources through legitimate network scanning activities. The flaw exists in the fundamental design of the connection management system, which fails to implement proper session throttling or rate limiting controls that would normally prevent a single source from overwhelming the system's capacity to handle concurrent connections.
The technical implementation of this vulnerability stems from the lack of maximum concurrent session limits within the NetScreen firewall's architecture. When an attacker performs a port scan against external networks from within a trusted network segment, the firewall processes each connection attempt without enforcing any upper bounds on concurrent sessions. This allows the attacker to establish multiple simultaneous connections that gradually deplete the system's available connection slots until no resources remain for legitimate traffic processing. The vulnerability operates at the network layer where connection tracking and session management occur, making it particularly dangerous as it can be executed from within the trusted network perimeter where such attacks might otherwise go undetected.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise the entire network infrastructure's availability and reliability. When a system becomes exhausted of available connections, legitimate users and applications cannot establish new connections to external resources, effectively creating a complete service disruption. This scenario is particularly concerning in enterprise environments where firewalls serve as critical gateways for network communication, as it can lead to cascading failures affecting multiple business applications and services. The vulnerability also demonstrates poor resource management practices that can result in extended downtime and significant operational costs associated with service restoration and security remediation.
The exploitation of this vulnerability aligns with several tactics described in the attack pattern taxonomy, particularly those involving resource exhaustion and denial of service attacks that target fundamental system capabilities. From a cybersecurity perspective, this vulnerability represents a classic example of inadequate access control and resource management within network security devices, where the absence of proper session limiting mechanisms creates an attack surface that can be easily exploited by malicious actors. The flaw specifically relates to weakness categories identified in CWE-400, which addresses "Uncontrolled Resource Consumption," and demonstrates how insufficient input validation and resource management can lead to system-wide availability issues.
Mitigation strategies for CVE-2002-0234 require immediate implementation of session limiting configurations within the NetScreen firewall system. Organizations should implement maximum session limits that prevent any single source from consuming excessive connection resources, typically through the configuration of connection rate limiting and session tracking parameters. The most effective approach involves upgrading to ScreenOS version 2.6.1 or later, which includes proper session management controls and resource limiting capabilities. Network administrators should also implement additional monitoring and alerting mechanisms to detect unusual connection patterns that might indicate exploitation attempts, while establishing proper network segmentation to limit the attack surface available to potential malicious actors within trusted network segments.