CVE-1999-0426 in Linux
Summary
by MITRE
The default permissions of /dev/kmem in Linux versions before 2.0.36 allows IP spoofing.
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Analysis
by VulDB Data Team • 04/18/2026
The vulnerability described in CVE-1999-0426 represents a critical security flaw in early linux kernel versions that fundamentally compromised network integrity and system security. This issue stems from the improper default permissions assigned to the /dev/kmem device file, which serves as a direct interface to physical memory in the kernel space. The vulnerability specifically affects linux kernel versions prior to 2.0.36, making it a legacy issue that highlights the evolution of kernel security practices over time. The flaw enables unauthorized users to manipulate network packet transmission by leveraging direct access to kernel memory structures that control network operations.
The technical implementation of this vulnerability exploits the fact that /dev/kmem was accessible with overly permissive permissions, allowing regular users to read and write directly to kernel memory addresses. This direct memory access capability enables attackers to modify network stack parameters, manipulate routing tables, and alter packet processing behavior in real-time. The specific mechanism involves modifying the kernel's network packet handling routines to create false network addresses or manipulate packet headers, which constitutes a form of IP spoofing. The vulnerability operates at the kernel level, making it particularly dangerous as it bypasses normal user-space security controls and operates with the highest privilege level available to the system.
The operational impact of this vulnerability extends far beyond simple network manipulation, as it fundamentally undermines network security protocols and trust mechanisms. An attacker with access to /dev/kmem can not only spoof IP addresses but can also modify network configuration parameters, disable security features, and potentially gain deeper system access. This capability directly violates the principle of least privilege and enables man-in-the-middle attacks, network disruption, and data interception. The vulnerability represents a classic case of insufficient privilege separation and inadequate access controls in kernel device management, creating a pathway for attackers to compromise network integrity and system confidentiality. This issue falls under the broader category of privilege escalation vulnerabilities and aligns with CWE-264, which addresses permissions, privileges, and access controls.
The mitigation strategies for this vulnerability primarily involve updating to linux kernel versions 2.0.36 or later, where proper permissions were implemented for /dev/kmem and other critical kernel devices. System administrators should also implement additional security measures such as disabling unnecessary kernel device access, implementing proper file system permissions, and monitoring for unauthorized access attempts to kernel memory interfaces. The solution addresses the root cause by ensuring that kernel devices are properly protected through access control lists and privilege management. This vulnerability demonstrates the importance of maintaining up-to-date kernel versions and proper system hardening practices, as outlined in various security frameworks including the MITRE ATT&CK matrix where such kernel-level access violations would be categorized under privilege escalation techniques. Organizations should also implement comprehensive monitoring and logging of kernel device access to detect potential exploitation attempts and maintain audit trails for security incident response.