CVE-2002-0060 in Linux
Summary
by MITRE
IRC connection tracking helper module in the netfilter subsystem for Linux 2.4.18-pre9 and earlier does not properly set the mask for conntrack expectations for incoming DCC connections, which could allow remote attackers to bypass intended firewall restrictions.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2002-0060 represents a critical flaw in the Linux kernel's netfilter subsystem that specifically affects the IRC connection tracking helper module. This issue manifests in kernel versions up to and including 2.4.18-pre9 where the conntrack subsystem fails to properly configure the mask for connection tracking expectations when handling incoming DCC (Direct Client-to-Client) connections. DCC connections are commonly used in Internet Relay Chat protocols for file transfers, voice communications, and direct messaging between clients. The improper mask configuration creates a pathway for remote attackers to exploit the firewall restrictions that are typically enforced by the netfilter framework.
The technical root cause of this vulnerability lies in the conntrack expectation mechanism within the netfilter subsystem. When a DCC connection is established, the kernel creates expectation entries that define the expected characteristics of the return traffic. The flaw occurs because the mask value used to define these expectations is not correctly set, allowing attackers to manipulate the connection tracking state. This improper mask handling enables attackers to craft packets that bypass the normal connection tracking validation, effectively creating a tunnel through firewall restrictions. The vulnerability specifically impacts the IRC protocol's DCC functionality where clients establish direct connections for file transfers or other media exchanges.
From an operational impact perspective, this vulnerability creates a significant security risk for systems running affected kernel versions. Attackers can exploit this weakness to bypass firewall rules that are designed to prevent unauthorized access to internal networks or specific services. The implications extend beyond simple packet filtering as the vulnerability allows for potential reconnaissance and lateral movement within network environments. Network administrators who rely on netfilter-based firewalls for security enforcement face a critical gap in their protection mechanisms, as the vulnerability undermines the fundamental principle of connection tracking that ensures proper stateful packet filtering. The attack vector is particularly concerning because it leverages legitimate protocol behavior rather than exploiting application-level flaws, making detection more challenging.
The vulnerability aligns with CWE-119 which addresses "Improper Access of a Resource via Pointer Dereference" and CWE-121 which deals with "Stack-based Buffer Overflow". From an ATT&CK framework perspective, this vulnerability maps to T1046 for Network Service Scanning and T1562.007 for "Tunneling/Interception' where attackers can establish unauthorized communication channels. The exploitation pattern follows T1071.004 for Application Layer Protocol: DNS where attackers may use the bypassed connections to establish covert communication channels. Organizations should implement immediate mitigations including kernel updates to versions 2.4.18-pre10 or later where the fix has been implemented. Additionally, network administrators should review their firewall rules to ensure that DCC connections are properly restricted at the application layer and consider implementing additional network segmentation. The fix typically involves correcting the mask value assignment in the conntrack expectation handling code to properly validate incoming DCC connection parameters. Regular monitoring for unusual connection patterns and implementing intrusion detection systems can help detect potential exploitation attempts. Organizations should also consider implementing protocol-specific controls that limit DCC functionality at the application level, as this provides defense-in-depth against such kernel-level vulnerabilities.