CVE-1999-0903 in AIX
Summary
by MITRE
genfilt in the AIX Packet Filtering Module does not properly filter traffic to destination ports greater than 32767.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0903 resides within the AIX Packet Filtering Module's genfilt component, representing a critical flaw in network traffic filtering mechanisms. This issue specifically impacts IBM's AIX operating system and demonstrates a fundamental failure in how the packet filtering system handles destination port numbers exceeding the 32767 threshold. The problem stems from improper validation and filtering logic that fails to adequately process high-numbered ports, creating potential security gaps in network traffic control.
The technical root cause of this vulnerability lies in the improper handling of 16-bit port number fields within network packets. Standard TCP and UDP port numbers are represented using 16-bit fields, which theoretically support values from 0 to 65535. However, the genfilt module in AIX exhibits flawed behavior when processing destination ports above 32767, effectively bypassing proper filtering mechanisms. This condition creates a scenario where traffic destined for high-numbered ports may be incorrectly allowed through the firewall or network filter, potentially enabling unauthorized access or traffic manipulation. The vulnerability specifically affects the packet filtering logic that should enforce access control policies based on destination port numbers, creating a gap in the security model that could be exploited by attackers.
The operational impact of this vulnerability extends beyond simple network access control failures, potentially enabling sophisticated attack vectors that leverage the filtering bypass. An attacker could exploit this weakness to direct traffic through network filters that were designed to block specific port ranges, effectively circumventing security controls. This flaw particularly impacts systems where the packet filtering module is used to enforce network segmentation, protect sensitive services, or implement access control policies based on port-based restrictions. The vulnerability creates a persistent security gap that could allow malicious actors to bypass network security controls without detection, potentially leading to unauthorized data access, service disruption, or further compromise of network resources.
Mitigation strategies for this vulnerability should focus on immediate system updates and configuration adjustments to address the filtering logic flaw. Organizations should implement the latest AIX security patches provided by IBM to correct the genfilt module behavior and ensure proper handling of destination port numbers across the full 16-bit range. Network administrators should also consider implementing additional security controls such as intrusion detection systems, network monitoring tools, and supplementary firewall rules to detect and prevent exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and represents a clear violation of secure coding practices that should prevent integer overflow or underflow conditions in network filtering components. From an ATT&CK framework perspective, this vulnerability maps to techniques involving network infiltration and privilege escalation through exploitation of security controls, emphasizing the need for comprehensive network security monitoring and robust access control implementations.