CVE-2008-3686 in Linux
Summary
by MITRE
The rt6_fill_node function in net/ipv6/route.c in Linux kernel 2.6.26-rc4, 2.6.26.2, and possibly other 2.6.26 versions, allows local users to cause a denial of service (kernel OOPS) via IPv6 requests when no IPv6 input device is in use, which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability described in CVE-2008-3686 represents a critical kernel-level flaw in the Linux networking subsystem that affects versions 2.6.26-rc4, 2.6.26.2, and potentially other variants within the 2.6.26 kernel series. This issue resides within the rt6_fill_node function located in the net/ipv6/route.c file, which handles IPv6 routing table operations. The vulnerability manifests when the kernel processes IPv6 requests in scenarios where no IPv6 input device is actively configured or available for processing. This specific condition creates a scenario where the kernel attempts to dereference a NULL pointer, leading to an immediate kernel panic or OOPS condition that effectively crashes the system.
The technical exploitation of this vulnerability occurs through a specific race condition in the IPv6 routing subsystem where the rt6_fill_node function fails to properly validate the existence of an input device before attempting to access routing table entries. When no IPv6 input device is present in the system configuration, the function proceeds to access memory locations that have not been properly initialized, resulting in a NULL pointer dereference. This type of vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The flaw represents a classic case of inadequate input validation and error handling within kernel space operations, where the absence of proper null checks leads to system instability and complete service disruption.
The operational impact of this vulnerability extends beyond simple denial of service as it can be exploited by local users with minimal privileges to cause complete system crashes. The kernel OOPS condition generated by this vulnerability results in immediate system unresponsiveness, requiring manual reboot to restore normal operation. This makes the vulnerability particularly dangerous in production environments where system availability is critical, as attackers can effectively render systems unusable without requiring elevated privileges. The attack vector is particularly concerning because it only requires local access to the system, making it possible for malicious users with basic user accounts to cause significant disruption. This vulnerability aligns with ATT&CK technique T1499.004 which describes the use of system shutdown/reboot attacks to deny service, though in this case the impact is achieved through kernel-level memory corruption rather than direct power management manipulation.
Mitigation strategies for this vulnerability must address both immediate system protection and long-term kernel security hardening. The most effective immediate solution involves applying the appropriate kernel security patches released by the Linux kernel development team, which include proper null pointer validation in the rt6_fill_node function. System administrators should also implement monitoring solutions to detect unusual network traffic patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing network segmentation and access controls to limit local user privileges where possible, reducing the attack surface for this type of vulnerability. The fix implemented in subsequent kernel versions demonstrates the importance of comprehensive input validation in kernel space code and serves as a reminder that even seemingly minor validation checks can prevent catastrophic system failures.