CVE-1999-0770 in Host
Summary
by MITRE
Firewall-1 sets a long timeout for connections that begin with ACK or other packets except SYN, allowing an attacker to conduct a denial of service via a large number of connection attempts to unresponsive systems.
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Analysis
by VulDB Data Team • 08/09/2024
The vulnerability described in CVE-1999-0770 affects Check Point Firewall-1, a widely deployed network security solution that implements stateful packet inspection and firewall capabilities. This flaw represents a classic denial of service vulnerability that exploits the firewall's connection tracking mechanisms and timeout behaviors. The issue specifically targets how Firewall-1 handles TCP connections that begin with ACK packets or other non-SYN packets, which are typically not part of standard TCP handshake sequences. When such connections are initiated, the firewall establishes a long timeout period for these connections, creating a resource exhaustion scenario that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from Firewall-1's connection state management system, which maintains tracking information for active connections in memory. When a TCP connection begins with an ACK packet rather than the standard SYN packet, the firewall's state machine fails to properly categorize this as an invalid or malformed connection attempt. Instead, it creates a connection entry with an extended timeout period, typically measured in minutes rather than seconds. This behavior violates the fundamental principle of connection tracking where invalid or unexpected connection attempts should be quickly discarded to prevent resource accumulation. The vulnerability directly maps to CWE-400, which covers "Uncontrolled Resource Consumption" and specifically addresses the improper handling of connection states in network security devices. The flaw essentially creates a memory leak scenario where connection tracking tables fill up with stale entries that remain active for extended periods.
The operational impact of this vulnerability is significant for organizations relying on Firewall-1 for network protection, as it provides a straightforward method for conducting denial of service attacks against target systems. An attacker can exploit this weakness by sending a large volume of TCP packets that begin with ACK flags to unresponsive or non-existent systems behind the firewall. Each such packet triggers the creation of a long-lived connection entry in the firewall's state table, consuming memory resources and potentially leading to complete system exhaustion. This attack vector is particularly dangerous because it requires minimal resources from the attacker while potentially causing maximum disruption to the target network infrastructure. The vulnerability demonstrates a critical flaw in the firewall's packet processing logic that fails to properly validate connection initiation sequences, which is a fundamental security requirement according to the principle of least privilege and proper input validation. Organizations using Firewall-1 may experience complete denial of service conditions where legitimate connection attempts are blocked due to exhausted connection tracking resources.
Mitigation strategies for this vulnerability should focus on both immediate configuration changes and long-term architectural improvements. Network administrators should implement connection tracking limits and timeout values that prevent excessive resource consumption, ensuring that the firewall does not maintain connection entries for extended periods. The recommended approach involves configuring shorter timeout values for non-SYN connections and implementing rate limiting mechanisms to prevent flood attacks from overwhelming the connection tracking system. Additionally, organizations should consider implementing intrusion detection systems that can identify and block suspicious connection patterns that match the vulnerability characteristics. The ATT&CK framework's T1498 technique for "Network Denial of Service" encompasses this type of attack, where adversaries exploit weaknesses in network infrastructure to cause service disruption. Organizations should also review their firewall configuration policies to ensure that only legitimate TCP connections are allowed to establish long-lived states, while malformed or unexpected connection attempts are quickly discarded. The vulnerability highlights the importance of proper state machine implementation in network security devices and reinforces the need for regular security assessments of firewall configurations to prevent resource exhaustion attacks.