CVE-2005-3809 in Linux
Summary
by MITRE
The nfattr_to_tcp function in ip_conntrack_proto_tcp.c in ctnetlink in Linux kernel 2.6.14 up to 2.6.14.3 allows attackers to cause a denial of service (kernel oops) via an update message without private protocol information, which triggers a null dereference.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability described in CVE-2005-3809 represents a critical denial of service flaw within the Linux kernel's connection tracking subsystem. This issue specifically affects the ctnetlink module which handles netfilter connection tracking for tcp protocol connections. The vulnerability stems from improper handling of update messages that lack private protocol information, creating a scenario where the kernel's tcp connection tracking mechanism fails catastrophically. The flaw exists in the nfattr_to_tcp function located within the ip_conntrack_proto_tcp.c file, which is part of the broader netfilter framework that manages network packet filtering and connection tracking. When an attacker sends a malformed update message through the netlink interface without providing the required private protocol data, the kernel's processing logic encounters a null pointer dereference that results in an immediate kernel oops and system crash. This type of vulnerability directly impacts the stability and availability of network services running on affected Linux systems, as the kernel becomes unresponsive when processing such malicious packets.
The technical implementation of this vulnerability can be categorized under CWE-476 as a NULL pointer dereference, which occurs when the kernel attempts to access a memory location through a pointer that has not been properly initialized or validated. The flaw demonstrates a classic lack of input validation within the kernel's connection tracking subsystem, where the function assumes that certain protocol-specific data structures will always be present in update messages. This oversight creates a path where malicious actors can exploit the absence of expected data fields to trigger kernel panics. The vulnerability operates at the kernel level and requires no special privileges to exploit, making it particularly dangerous as it can be triggered by any network entity capable of sending crafted netlink messages to the system. The specific function nfattr_to_tcp processes attributes received from userspace applications through the ctnetlink interface, but fails to properly validate whether the necessary private protocol information exists before attempting to dereference pointers to this data.
The operational impact of CVE-2005-3809 extends beyond simple service disruption to potentially compromise entire network infrastructure. Systems running Linux kernels version 2.6.14 through 2.6.14.3 are vulnerable to this attack, which can be exploited to cause complete system crashes through kernel oops conditions. This denial of service vulnerability affects any network service that relies on the kernel's connection tracking capabilities, including firewalls, routers, and network appliances that utilize netfilter for packet filtering and connection management. The attack vector is particularly concerning because it can be executed remotely through network communication channels, allowing attackers to cause persistent system instability without requiring physical access or elevated privileges. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, where adversaries exploit weaknesses in system components to disrupt network services. The kernel oops generated by this vulnerability can also potentially expose sensitive kernel memory information, though the primary impact remains service disruption rather than information disclosure.
Mitigation strategies for CVE-2005-3809 focus on both immediate patching and operational security measures. The most effective solution involves upgrading to a patched version of the Linux kernel, specifically versions 2.6.14.4 or later where the vulnerability has been addressed through proper null pointer validation in the nfattr_to_tcp function. System administrators should implement regular kernel updates as part of their security maintenance procedures to prevent exploitation of known vulnerabilities. Network-level mitigations include implementing firewall rules that restrict access to the netlink interface and limiting the types of messages that can be sent to the connection tracking subsystem. Additionally, monitoring for unusual patterns of connection tracking updates can help detect potential exploitation attempts. The vulnerability demonstrates the importance of robust input validation in kernel space code and highlights the need for comprehensive testing of edge cases in network protocol handling code. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious netlink traffic patterns, as this vulnerability can be used as part of broader network attack campaigns targeting system stability and availability.