CVE-2007-3720 in Linux
Summary
by MITRE
The process scheduler in the Linux kernel 2.4 performs scheduling based on CPU billing gathered from periodic process sampling ticks, which allows local users to cause a denial of service (CPU consumption) by performing voluntary nanosecond sleeps that result in the process not being active during a clock interrupt, as described in "Secretly Monopolizing the CPU Without Superuser Privileges."
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability described in CVE-2007-3720 resides within the Linux kernel version 2.4 scheduling mechanism, specifically targeting how the kernel tracks CPU usage through periodic process sampling ticks. This flaw represents a significant design weakness in the kernel's process accounting system that operates under the principle of CPU billing based on clock interrupts. The vulnerability allows local attackers to exploit the scheduling algorithm by utilizing voluntary nanosecond sleeps that deliberately avoid triggering clock interrupts during their execution period. This manipulation occurs because the kernel's scheduler relies on these periodic sampling events to accurately measure and allocate CPU time to different processes, creating a fundamental mismatch between the actual CPU consumption and the recorded accounting.
The technical exploitation of this vulnerability stems from the kernel's reliance on timer-based sampling for process accounting, which creates an opportunity for malicious processes to consume CPU resources without proper billing recognition. When a process performs voluntary nanosecond sleeps, it effectively becomes inactive during clock interrupt periods, causing the scheduler to misattribute CPU time and potentially leading to a situation where the malicious process can monopolize system resources without detection. This behavior directly violates the fundamental principles of fair scheduling and resource allocation that the Linux kernel's process management system is designed to enforce, creating a scenario where legitimate processes may be starved of CPU time while the malicious process continues to consume resources undetected.
The operational impact of this vulnerability extends beyond simple resource consumption to represent a serious threat to system stability and performance. Local users can leverage this flaw to cause denial of service conditions where normal system operations become degraded or completely halted, as the scheduler's accounting becomes increasingly inaccurate and the system's ability to maintain fair resource distribution deteriorates. The vulnerability's exploitation does not require special privileges beyond standard user access, making it particularly dangerous as it can be abused by any local user to compromise system integrity. This type of attack falls under the category of resource exhaustion attacks that target the kernel's fundamental scheduling mechanisms, potentially leading to cascading failures throughout the system.
This vulnerability demonstrates a clear violation of security principles related to process accounting and resource management, aligning with CWE-254 in the Common Weakness Enumeration which addresses security weaknesses in resource management. The attack pattern corresponds to techniques described in the MITRE ATT&CK framework under process injection and privilege escalation categories, specifically targeting the kernel's scheduling subsystem. The flaw represents a design weakness in the kernel's accounting system that was later addressed through improvements in kernel scheduling algorithms and more robust timer handling mechanisms. Organizations should implement kernel updates and patches that correct the scheduling accounting mechanisms, while also monitoring for suspicious CPU usage patterns that might indicate exploitation attempts. System administrators should consider implementing resource limits and monitoring tools that can detect abnormal process behavior, particularly focusing on processes that exhibit unusual sleeping patterns or CPU consumption that deviates from normal accounting expectations.