CVE-2003-0467 in IPTables
Summary
by MITRE
Unknown vulnerability in ip_nat_sack_adjust of Netfilter in Linux kernels 2.4.20, and some 2.5.x, when CONFIG_IP_NF_NAT_FTP or CONFIG_IP_NF_NAT_IRC is enabled, or the ip_nat_ftp or ip_nat_irc modules are loaded, allows remote attackers to cause a denial of service (crash) in systems using NAT, possibly due to an integer signedness error.
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Analysis
by VulDB Data Team • 03/08/2021
The vulnerability described in CVE-2003-0467 represents a critical flaw within the Linux kernel's Netfilter framework, specifically within the ip_nat_sack_adjust function that handles TCP selective acknowledgment adjustments during network address translation operations. This issue affects kernel versions 2.4.20 and certain 2.5.x releases, creating a significant security concern for systems implementing NAT functionality. The vulnerability manifests when either the CONFIG_IP_NF_NAT_FTP or CONFIG_IP_NF_NAT_IRC kernel configuration options are enabled, or when the corresponding ip_nat_ftp and ip_nat_irc kernel modules are actively loaded, indicating that the flaw is specifically tied to NAT implementations that handle FTP and IRC protocol translations.
The technical root cause of this vulnerability stems from an integer signedness error within the ip_nat_sack_adjust function, which processes TCP selective acknowledgment data structures during NAT operations. When a malicious remote attacker sends specially crafted TCP packets containing selective acknowledgment information, the function fails to properly handle the signed integer values, leading to potential integer overflow conditions or improper memory handling. This flaw operates at the kernel level within the network packet processing pipeline, specifically affecting how the kernel manages TCP sequence numbers and acknowledgment information when translating addresses for FTP and IRC connections. The vulnerability is classified under CWE-191 as an integer underflow or overflow, and more specifically as CWE-129 as an improper validation of array index, since the error occurs during the processing of TCP sequence number adjustments.
The operational impact of this vulnerability is severe, as it allows remote attackers to trigger a system crash or denial of service condition on vulnerable systems. When exploited, the vulnerability causes the kernel to crash, resulting in a complete system halt that requires manual intervention to restore normal operation. This affects systems that rely on NAT functionality for network connectivity, particularly those running Linux kernels with FTP or IRC NAT support enabled. The vulnerability is particularly dangerous in network environments where NAT is commonly used, such as corporate networks, internet service provider infrastructure, and home routers that implement NAT for network address translation. The attack vector requires only that a remote attacker send specific TCP packets to a system with NAT enabled, making it relatively easy to exploit and potentially affecting a large number of systems.
Mitigation strategies for this vulnerability involve multiple approaches that address both immediate protection and long-term system hardening. The most effective immediate solution is to disable the problematic kernel configuration options CONFIG_IP_NF_NAT_FTP and CONFIG_IP_NF_NAT_IRC when they are not actively required, or to avoid loading the ip_nat_ftp and ip_nat_irc kernel modules altogether. System administrators should also consider upgrading to patched kernel versions that contain fixes for this specific integer signedness error, typically found in kernel versions released after the vulnerability was identified. Network administrators can implement firewall rules to limit exposure to the affected protocols, though this approach provides only partial protection since the vulnerability exists within the kernel's core NAT processing functionality. The ATT&CK framework categorizes this vulnerability under T1499.004 as Network Denial of Service, specifically targeting the kernel's network processing capabilities. Additionally, organizations should implement monitoring systems to detect unusual network traffic patterns that might indicate exploitation attempts, and maintain up-to-date kernel security patches to prevent similar vulnerabilities from being exploited in the future.