CVE-2008-5713 in Linux
Summary
by MITRE
The __qdisc_run function in net/sched/sch_generic.c in the Linux kernel before 2.6.25 on SMP machines allows local users to cause a denial of service (soft lockup) by sending a large amount of network traffic, as demonstrated by multiple simultaneous invocations of the Netperf benchmark application in UDP_STREAM mode.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability described in CVE-2008-5713 represents a critical soft lockup issue affecting Linux kernel versions prior to 2.6.25, specifically on symmetric multiprocessing systems. This flaw resides within the network scheduling subsystem where the __qdisc_run function fails to properly handle high-volume network traffic scenarios, creating a condition that can be exploited to cause system-wide denial of service. The vulnerability demonstrates how network processing can become a vector for system instability when traffic volumes exceed expected thresholds, particularly under concurrent processing conditions typical in high-performance networking environments.
The technical root cause of this vulnerability stems from improper handling of the queuing discipline execution loop in the kernel's network subsystem. When multiple simultaneous network connections or high-volume traffic streams are processed through the generic scheduler, the __qdisc_run function enters an unbounded loop that prevents the system from performing other essential tasks. This occurs because the function does not adequately implement time-slicing or resource management controls when processing packets, allowing a single traffic stream to monopolize CPU resources and effectively freeze the system's responsiveness. The issue is particularly pronounced in SMP environments where multiple processors may be simultaneously affected by the resource exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete system freeze conditions that can persist until manual intervention occurs. Attackers can trigger this condition by generating sustained high-volume UDP traffic through multiple concurrent connections, effectively creating a soft lockup scenario where the system becomes unresponsive to user input and network operations. The demonstration using Netperf in UDP_STREAM mode illustrates how legitimate network benchmarking tools can inadvertently become weaponized to exploit this vulnerability, making it particularly concerning for network administrators and system operators who may unknowingly trigger the condition during performance testing or normal operations.
This vulnerability maps directly to CWE-772, which addresses insufficient resource management, and aligns with ATT&CK technique T1499.001 for network denial of service. The attack pattern follows a classic resource exhaustion methodology where network bandwidth and CPU cycles are consumed to the point of system paralysis. The vulnerability demonstrates the importance of proper queuing discipline implementation in kernel networking code and highlights how seemingly routine network operations can expose fundamental design flaws in system resource management. Organizations using Linux systems prior to kernel version 2.6.25 should prioritize immediate patching to address this vulnerability, as the impact of exploitation can result in complete system unavailability and potential data loss during the lockup period.
Mitigation strategies should include immediate kernel version upgrades to 2.6.25 or later, where the patch addresses the queuing discipline handling through improved resource management and time-slicing mechanisms. Network administrators should also implement traffic monitoring and rate limiting policies to detect and prevent abnormal traffic patterns that could trigger the vulnerability. Additionally, system administrators should consider implementing network segmentation and bandwidth controls to limit the impact of potentially malicious traffic streams that could exploit similar resource management flaws in other kernel components. The vulnerability serves as a reminder of the critical importance of proper resource management in kernel-level networking code and the potential for network subsystem flaws to create system-wide stability issues.