CVE-2003-0393 in Privatefirewall
Summary
by MITRE
Privacyware Privatefirewall 3.0 does not block certain incoming packets when in "Filter Internet Traffic" or Deny Internet Traffic" modes, which allows remote attackers to identify running services via FIN scans or Xmas scans.
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Analysis
by VulDB Data Team • 06/14/2018
The vulnerability described in CVE-2003-0393 affects Privacyware Privatefirewall version 3.0, a network security application designed to protect systems from unauthorized network access. This weakness represents a significant flaw in the firewall's packet filtering implementation that directly impacts its ability to provide effective network security. The vulnerability specifically manifests when the firewall operates in either "Filter Internet Traffic" or "Deny Internet Traffic" modes, which are standard operational configurations for network protection. These modes are intended to block incoming network connections and prevent unauthorized access to the protected system, yet the flaw allows attackers to bypass these protections through specific scanning techniques.
The technical nature of this vulnerability stems from the firewall's incomplete packet processing logic that fails to properly handle certain types of TCP packets during connection state analysis. When the firewall operates in its designated protection modes, it should consistently block incoming packets that could reveal information about the system's network services. However, the implementation contains a gap that permits specific TCP packet patterns to pass through undetected, particularly those used in advanced scanning techniques. This failure occurs because the firewall's packet inspection mechanism does not adequately account for the FIN scan and Xmas scan methodologies that attackers employ to discover running services on target systems.
The operational impact of this vulnerability is substantial as it fundamentally undermines the firewall's core security function of service hiding and network protection. Remote attackers can leverage this weakness to conduct service discovery attacks using FIN scans or Xmas scans, which are sophisticated techniques that exploit specific TCP packet flags to determine whether network services are active on a target system. These scanning methods are particularly effective because they send packets with specific flag combinations that should normally be rejected by properly configured firewalls, yet this vulnerability allows them to pass through the Privatefirewall's filtering mechanisms. The result is that attackers can identify running services without being detected, potentially leading to further exploitation attempts.
This vulnerability aligns with CWE-652, which addresses "Improper Neutralization of Data within a Security Control," and represents a failure in proper packet filtering implementation that violates fundamental security principles. The attack pattern follows ATT&CK technique T1046, which involves network service scanning to identify running services and potential attack vectors. Organizations using Privacyware Privatefirewall 3.0 in production environments face significant risk as this vulnerability effectively creates a backdoor that allows unauthorized reconnaissance without triggering any security alerts. The flaw essentially provides attackers with a method to map the network service landscape of protected systems, potentially enabling more sophisticated attacks such as service enumeration, vulnerability assessment, and targeted exploitation of identified services. This weakness demonstrates the critical importance of comprehensive packet filtering logic and proper stateful inspection in network security implementations.
The mitigation approach for this vulnerability requires immediate patching or replacement of the affected Privacyware Privatefirewall 3.0 software, as the flaw represents a fundamental design weakness in the packet filtering engine. Organizations should also implement additional network monitoring to detect unusual scanning patterns and consider deploying complementary security controls such as intrusion detection systems or network segmentation to limit the impact of such reconnaissance activities. The vulnerability highlights the necessity of thorough testing and validation of security controls, particularly in packet filtering and stateful inspection mechanisms, to ensure that all potential attack vectors are properly addressed. Security teams should also review their network security policies and ensure that multiple layers of protection are implemented to compensate for individual control failures, as this vulnerability demonstrates how a single implementation flaw can compromise the entire security posture of a protected network environment.