CVE-2007-5093 in Linux
Summary
by MITRE
The disconnect method in the Philips USB Webcam (pwc) driver in Linux kernel 2.6.x before 2.6.22.6 "relies on user space to close the device," which allows user-assisted local attackers to cause a denial of service (USB subsystem hang and CPU consumption in khubd) by not closing the device after the disconnect is invoked. NOTE: this rarely crosses privilege boundaries, unless the attacker can convince the victim to unplug the affected device.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability described in CVE-2007-5093 represents a significant flaw in the Philips USB Webcam (pwc) driver implementation within the Linux kernel version 2.6.x series prior to 2.6.22.6. This issue stems from a fundamental design oversight in how the driver handles device disconnection events, creating a potential for denial of service conditions that can severely impact system stability and resource utilization. The problem manifests specifically within the disconnect method of the pwc driver, which demonstrates a critical dependency on proper user space handling of device closure operations.
The technical root cause of this vulnerability lies in the driver's improper handling of USB device disconnection sequences where the kernel component fails to adequately manage the device state transition. When a disconnect event is triggered, the pwc driver relies entirely on user space applications to properly close and release the device resources, rather than implementing proper kernel-level resource cleanup mechanisms. This design flaw creates a scenario where if user space applications fail to close the device handle after disconnection, the USB subsystem becomes trapped in an inconsistent state. The khubd process, which manages USB hub events and device state transitions, becomes overloaded with pending operations and consumes excessive CPU cycles while attempting to process the orphaned device references.
From an operational perspective, this vulnerability creates a substantial risk for local attackers who can manipulate the USB subsystem through user-assisted means. The attack vector requires minimal privileges since it operates within the local user context, though it typically does not cross privilege boundaries unless an attacker can successfully convince a victim to unplug the affected USB webcam device. The resulting denial of service conditions can cause complete USB subsystem hangs, rendering USB devices non-responsive and potentially affecting other system functions that depend on USB communication. The CPU consumption spike in the khubd process can lead to system performance degradation and in severe cases, complete system unresponsiveness.
The impact of this vulnerability aligns with CWE-404, which addresses improper resource management, and demonstrates characteristics consistent with ATT&CK technique T1499.004 for endpoint denial of service. The vulnerability represents a classic case of resource leak and improper state management within kernel space, where the driver fails to properly clean up resources during device disconnection events. The attack requires only local user access and can be executed through standard USB device manipulation techniques, making it particularly concerning for systems where USB devices are frequently connected and disconnected. The lack of proper kernel-level resource management creates an opportunity for attackers to exhaust system resources and cause sustained denial of service conditions.
Mitigation strategies for this vulnerability include applying the kernel patch released with version 2.6.22.6, which implements proper resource cleanup during device disconnection events. System administrators should ensure all affected kernel versions are updated promptly and monitor USB subsystem behavior for signs of resource exhaustion. Additionally, implementing proper device management policies and ensuring user applications properly handle device closure operations can help reduce the attack surface. The vulnerability serves as a reminder of the critical importance of proper resource management in kernel drivers and highlights the need for comprehensive testing of device disconnection scenarios to prevent similar issues in other USB driver implementations.