CVE-1999-0770 is a vulnerability found in Check Point's Firewall-1 product, specifically versions 3.0 and 4.0. The issue arises from the firewall's handling of connection timeouts for packets that begin with an ACK flag or other TCP flags except SYN. Normally, TCP connections start with a SYN packet, and firewalls track these connection states to manage resources efficiently. However, Firewall-1 sets an unusually long timeout for connections initiated by packets other than SYN, such as ACK packets. This behavior allows an attacker to exploit the firewall by sending a large number of connection attempts to unresponsive systems using these non-SYN packets. Because the firewall maintains these connection states for an extended period, it can exhaust the firewall's resources, leading to a denial of service (DoS) condition. The vulnerability does not affect confidentiality or integrity but impacts availability by potentially overwhelming the firewall's connection tracking capabilities. There is no patch available for this issue, and no known exploits have been reported in the wild. The CVSS v2 score is 2.1, indicating a low severity primarily due to the local attack vector and the requirement that the attacker can send packets to the firewall, but no authentication is needed. This vulnerability is dated from 1999 and affects legacy versions of Firewall-1, which may still be in use in some environments.

For European organizations, the primary impact of this vulnerability is the risk of denial of service against network perimeter defenses if they are still using the affected versions of Check Point Firewall-1 (3.0 or 4.0). Such a DoS could disrupt business operations by preventing legitimate traffic from passing through the firewall, potentially causing downtime or degraded network performance. While modern firewalls and updated versions have likely mitigated this issue, legacy systems in critical infrastructure, government, or industrial environments may still be vulnerable. The impact is limited to availability and does not compromise data confidentiality or integrity. However, any disruption to firewall services can have cascading effects on network security posture and business continuity. Given the age of the vulnerability and lack of patches, organizations relying on these older firewall versions face a persistent risk if they have not migrated to newer solutions.

Since no patch is available for this vulnerability, European organizations should prioritize upgrading or replacing affected Firewall-1 versions (3.0 and 4.0) with current, supported versions of Check Point firewalls or alternative modern firewall solutions. Network administrators should audit their perimeter devices to identify any legacy firewall deployments and plan for their decommissioning. In the interim, organizations can implement network-level rate limiting or filtering to detect and block abnormal volumes of ACK or non-SYN packets targeting unresponsive systems to reduce the risk of resource exhaustion. Monitoring firewall logs for unusual connection attempts and implementing intrusion detection systems (IDS) to alert on anomalous traffic patterns can help detect exploitation attempts. Additionally, segmenting critical network assets and applying strict access controls can limit the attack surface. Regular network security assessments and penetration testing should include checks for legacy vulnerabilities such as this one.