CVE-2021-30002 in Linux
Summary
by MITRE • 04/02/2021
An issue was discovered in the Linux kernel before 5.11.3 when a webcam device exists. video_usercopy in drivers/media/v4l2-core/v4l2-ioctl.c has a memory leak for large arguments, aka CID-fb18802a338b.
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Analysis
by VulDB Data Team • 04/07/2021
The vulnerability described in CVE-2021-30002 represents a critical memory management flaw within the Linux kernel's video4linux2 (v4l2) subsystem that specifically impacts webcam device functionality. This issue affects systems running Linux kernel versions prior to 5.11.3 and manifests when webcam hardware is present in the system. The vulnerability stems from improper handling of large argument structures within the video_usercopy function, which is part of the v4l2-ioctl.c file located in the drivers/media/v4l2-core directory. The flaw creates a memory leak condition that can be exploited through improper argument processing during video device ioctls.
The technical implementation of this vulnerability involves the video_usercopy function which is responsible for copying user-space data to kernel-space when handling video device ioctls. When large argument structures are passed to this function, the memory allocation process fails to properly release allocated memory resources, resulting in a gradual accumulation of memory leaks. This memory leak occurs specifically in the context of webcam device operations where large data structures are commonly passed during ioctl calls for video capture and control operations. The vulnerability is classified as a memory leak under CWE-401 and represents a failure in proper resource management within kernel space operations. The memory leak can be systematically exploited by repeatedly invoking video device ioctls with large arguments, leading to progressive memory consumption that can eventually cause system instability or denial of service conditions.
The operational impact of CVE-2021-30002 extends beyond simple resource exhaustion, as it creates a persistent vulnerability that can be leveraged for various malicious activities. Attackers can utilize this flaw to consume system memory resources over time, potentially leading to system crashes or degraded performance that affects legitimate users of webcam functionality. The vulnerability is particularly concerning in server environments or embedded systems where webcam devices may be present but not actively used, as the memory leak can occur passively without requiring active exploitation. From an operational security perspective, this vulnerability aligns with ATT&CK technique T1499.001 which involves resource exhaustion attacks targeting system memory. The flaw can be exploited to create persistent denial of service conditions, making it a significant concern for system administrators and security professionals responsible for maintaining kernel security.
Mitigation strategies for this vulnerability primarily focus on kernel version updates and system hardening measures. The most effective immediate solution involves upgrading to Linux kernel version 5.11.3 or later, where the memory leak has been addressed through proper memory management in the video_usercopy function. System administrators should also implement monitoring solutions to detect unusual memory consumption patterns that might indicate exploitation attempts. Additional defensive measures include restricting access to video device nodes through proper file permissions and implementing security frameworks such as SELinux or AppArmor to limit potential exploitation paths. The vulnerability demonstrates the importance of proper resource management in kernel space operations and highlights the need for comprehensive testing of ioctl handling functions. Organizations should also consider implementing automated patch management systems to ensure timely deployment of kernel security updates and maintain visibility into their systems' kernel versions to prevent exploitation of known vulnerabilities.