CVE-2007-3719 in Linux
Summary
by MITRE
The process scheduler in the Linux kernel 2.6.16 gives preference to "interactive" processes that perform voluntary sleeps, which allows local users to cause a denial of service (CPU consumption), as described in "Secretly Monopolizing the CPU Without Superuser Privileges."
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability identified as CVE-2007-3719 resides within the Linux kernel version 2.6.16 and specifically targets the process scheduler component that governs how system resources are allocated among competing processes. This flaw exploits the scheduler's algorithm designed to prioritize interactive processes, which are typically characterized by voluntary sleep operations that indicate user-facing applications such as desktop environments or terminal sessions. The scheduler's design intent was to improve user experience by ensuring responsive interfaces, but this mechanism became exploitable due to insufficient validation of process behavior patterns. The vulnerability operates under the Common Weakness Enumeration classification of CWE-20, which encompasses improper input validation, as the scheduler fails to properly verify that processes claiming to be interactive are actually behaving in an interactive manner. This weakness allows malicious users to manipulate the scheduler's decision-making process by creating artificial interactive behavior through voluntary sleep patterns, effectively tricking the kernel into prioritizing their processes over others.
The technical exploitation of this vulnerability occurs when a local user crafts a process that repeatedly performs voluntary sleeps while maintaining a high priority in the scheduler's interactive process queue. The scheduler, designed to favor processes that demonstrate interactive behavior, mistakenly identifies these artificial processes as legitimate interactive applications and grants them preferential treatment. This misclassification leads to a situation where the malicious process consumes an disproportionate amount of CPU time, effectively monopolizing system resources while other processes are starved of necessary processing cycles. The specific mechanism relies on the kernel's implementation of the Completely Fair Scheduler (CFS) which was still in development during this time period, though the core concept of prioritizing voluntary sleeps for interactive processes was already established. The vulnerability essentially represents a privilege escalation vector within the kernel's resource management system, allowing unprivileged users to manipulate system-wide scheduling decisions.
The operational impact of this vulnerability manifests as a denial of service condition where system performance degrades significantly or becomes completely unresponsive to legitimate user processes. Attackers can maintain persistent CPU consumption by creating a loop of voluntary sleeps that keeps their process in the interactive priority queue, causing the system to allocate most available CPU cycles to these artificial processes while legitimate applications struggle for resources. This behavior can be sustained indefinitely without requiring elevated privileges, making it particularly dangerous in multi-user environments where one user can potentially disrupt system operations for all users. The vulnerability affects systems running Linux kernel version 2.6.16 and earlier, where the scheduler's heuristics for identifying interactive processes were insufficiently robust to distinguish between genuine interactive applications and maliciously crafted processes. The impact extends beyond simple performance degradation to potentially complete system lockup, especially in scenarios where the scheduler's resource allocation becomes completely skewed toward the malicious processes.
Mitigation strategies for CVE-2007-3719 require both immediate kernel updates and implementation of additional system monitoring controls. The primary solution involves upgrading to a Linux kernel version that addresses this specific scheduling flaw, typically found in kernel versions 2.6.17 and later where the scheduler's interactive process detection mechanisms were improved. System administrators should also implement process monitoring tools that can detect unusual CPU consumption patterns and voluntary sleep behaviors that might indicate exploitation attempts. Additional mitigations include implementing resource limits through cgroups or ulimits to prevent any single process from consuming excessive CPU time, and establishing proper access controls to limit local user privileges where possible. The vulnerability demonstrates the importance of proper kernel security design and the need for comprehensive testing of scheduler algorithms against potential abuse scenarios. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and denial of service through system resource manipulation, specifically leveraging the kernel's scheduling subsystem as an attack vector. Organizations should also consider implementing process behavior analysis tools that can detect anomalous voluntary sleep patterns that deviate from normal interactive application behavior, providing an additional layer of defense against this specific class of exploitation.