CVE-2019-18809 in Linux
Summary
by MITRE
A memory leak in the af9005_identify_state() function in drivers/media/usb/dvb-usb/af9005.c in the Linux kernel through 5.3.9 allows attackers to cause a denial of service (memory consumption), aka CID-2289adbfa559.
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Analysis
by VulDB Data Team • 02/05/2024
The vulnerability identified as CVE-2019-18809 represents a critical memory management flaw within the Linux kernel's digital video broadcasting usb subsystem. This issue resides in the af9005_identify_state() function located within the drivers/media/usb/dvb-usb/af9005.c source file, affecting all kernel versions up to and including 5.3.9. The flaw manifests as a memory leak that occurs during the device identification process for certain DVB USB receivers, specifically those using the af9005 chipsets. The vulnerability is particularly concerning because it enables attackers to exploit the memory leak for denial of service attacks, where sustained exploitation can lead to progressive memory consumption that ultimately degrades system performance or causes complete system hang.
The technical mechanism behind this vulnerability involves improper memory allocation and deallocation within the device state identification routine. When the kernel attempts to identify and configure DVB USB devices using the af9005 chipset, the af9005_identify_state() function fails to properly release allocated memory resources during certain error conditions or state transitions. This memory leak occurs repeatedly with each device identification attempt, creating a cumulative effect that gradually consumes available system memory. The flaw is classified under CWE-401 as a failure to release memory resources, which directly impacts the system's ability to maintain stable operation over time. The vulnerability operates at the kernel level, making it particularly dangerous as it affects the core operating system functionality rather than user-space applications.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it creates a persistent threat to system stability and availability. Attackers can repeatedly trigger the memory leak condition through legitimate device enumeration processes, causing progressive memory consumption that may eventually lead to system crashes, application failures, or complete system lockups. This makes the vulnerability particularly dangerous in embedded systems, servers, or devices that rely on continuous operation where a denial of service condition could result in significant operational disruption. The attack surface is broad as any system running the affected kernel version and utilizing DVB USB devices with af9005 chipsets could be compromised, including media centers, set-top boxes, and digital television receivers. The vulnerability aligns with ATT&CK technique T1499.004 for resource exhaustion, where adversaries leverage system weaknesses to consume computational resources and cause service disruption.
Mitigation strategies for CVE-2019-18809 primarily focus on immediate kernel updates and system hardening measures. The most effective solution involves upgrading to a kernel version that contains the patched af9005.c implementation, typically kernel versions 5.4.0 and later where the memory leak has been addressed through proper memory management practices. System administrators should also implement monitoring solutions to detect unusual memory consumption patterns that may indicate exploitation attempts. Additionally, organizations should consider disabling unnecessary DVB USB device support when not actively required, reducing the attack surface. The patch implementation follows standard memory management best practices, ensuring that all allocated memory is properly freed regardless of execution path, thus addressing the root cause of the memory leak. Organizations should also establish regular patch management procedures to prevent similar vulnerabilities from accumulating in their systems.