CVE-2004-0596 in Linux
Summary
by MITRE
The Equalizer Load-balancer for serial network interfaces (eql.c) in Linux kernel 2.6.x up to 2.6.7 allows local users to cause a denial of service via a non-existent device name that triggers a null dereference.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability described in CVE-2004-0596 affects the Linux kernel's Equalizer Load-balancer implementation known as eql.c which manages serial network interfaces. This particular flaw exists within kernel versions 2.6.x up to and including 2.6.7, representing a critical security issue that impacts systems utilizing serial network load balancing capabilities. The vulnerability stems from improper input validation within the kernel's network interface handling mechanisms, specifically when processing device names for serial connections.
The technical flaw manifests as a null pointer dereference condition that occurs when the eql.c module receives a non-existent device name as input. When a local user provides an invalid device identifier to the load-balancer, the kernel code fails to properly validate the input before attempting to access memory locations associated with the device structure. This results in a kernel panic or system crash, effectively causing a denial of service condition that renders the affected system unstable and unresponsive to network traffic. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system.
The operational impact of this vulnerability extends beyond simple system instability as it can be leveraged to disrupt critical network services that rely on load-balanced serial connections. In enterprise environments where serial network interfaces are used for redundant connections or specific communication protocols, this flaw could lead to significant service interruptions. The local privilege escalation aspect means that even users without administrative rights could potentially cause system-wide disruptions, making it a particularly concerning issue for multi-user systems. Network administrators may find their load-balanced serial connections become unreliable or completely fail, affecting mission-critical communications.
The vulnerability aligns with CWE-476 which specifically addresses null pointer dereference conditions in software implementations. From an adversarial perspective, this flaw maps to ATT&CK technique T1499.004 which involves network denial of service attacks, though in this case the attack vector is through local system interaction rather than external network traffic. The root cause demonstrates poor input validation practices that violate fundamental security principles for kernel module development. System administrators should immediately implement kernel updates to address this vulnerability, as the fix typically involves adding proper validation checks before accessing device structures. Additionally, monitoring for unusual device name patterns or system crashes related to serial interfaces can help detect potential exploitation attempts. Organizations should also consider implementing additional access controls to limit local user privileges where possible, though the fundamental fix requires kernel-level patching to prevent the null pointer dereference condition from occurring in the first place.