CVE-2001-0402 in IPFilter
Summary
by MITRE
IPFilter 3.4.16 and earlier does not include sufficient session information in its cache, which allows remote attackers to bypass access restrictions by sending fragmented packets to a restricted port after sending unfragmented packets to an unrestricted port.
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Analysis
by VulDB Data Team • 01/19/2025
The vulnerability identified as CVE-2001-0402 represents a significant weakness in IPFilter version 3.4.16 and earlier implementations that directly impacts network access control mechanisms. This flaw resides in the session tracking system of IPFilter, which is a packet filtering and NAT implementation commonly used in unix-based systems including solaris and freebsd operating systems. The core issue stems from insufficient session information being maintained within the cache mechanism, creating a predictable gap in the firewall's ability to properly track and validate network connections across different packet transmission patterns.
The technical exploitation of this vulnerability occurs through a specific packet fragmentation attack pattern that exploits the cache's limited session tracking capabilities. Attackers can bypass access restrictions by strategically sending fragmented packets to a restricted port while simultaneously sending unfragmented packets to an unrestricted port. This technique leverages the fact that IPFilter's cache does not properly correlate fragmented packets with their corresponding session information, allowing malicious actors to establish connections that should otherwise be blocked by access control policies. The vulnerability specifically targets the session cache invalidation and correlation mechanisms that should maintain consistent state information across all packets belonging to the same network session.
The operational impact of this vulnerability extends beyond simple access bypass, as it fundamentally undermines the integrity of network security policies implemented through IPFilter. Network administrators who rely on IPFilter for access control and traffic management face the risk of unauthorized access to restricted resources, potentially leading to data breaches, system compromise, and unauthorized network operations. This vulnerability affects the fundamental trust model of network security by allowing attackers to exploit the gap in session tracking between fragmented and unfragmented packet delivery, creating a persistent backdoor that can be repeatedly exploited without detection. The impact is particularly severe in environments where IPFilter serves as a primary defense mechanism against unauthorized network access.
Mitigation strategies for CVE-2001-0402 require immediate implementation of IPFilter version 3.4.17 or later, which includes the necessary fixes to properly maintain session information in the cache mechanism. Network administrators should also implement additional monitoring and logging of fragmented packet traffic to detect potential exploitation attempts. The vulnerability aligns with CWE-284 Access Control Issues, specifically targeting improper access control through session tracking failures, and can be categorized under ATT&CK technique T1071.004 Application Layer Protocol: DNS, as it exploits network protocol handling to bypass security controls. Organizations should conduct comprehensive security assessments to identify any systems running vulnerable IPFilter versions and implement proper network segmentation to limit the potential impact of successful exploitation attempts.