CVE-2019-20811 in Linux
Summary
by MITRE • 01/25/2023
An issue was discovered in the Linux kernel before 5.0.6. In rx_queue_add_kobject() and netdev_queue_add_kobject() in net/core/net-sysfs.c, a reference count is mishandled, aka CID-a3e23f719f5c.
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Analysis
by VulDB Data Team • 03/05/2025
The vulnerability identified as CVE-2019-20811 represents a critical reference count management flaw within the Linux kernel's networking subsystem. This issue affects kernel versions prior to 5.0.6 and specifically targets the rx_queue_add_kobject() and netdev_queue_add_kobject() functions located in the net/core/net-sysfs.c file. The flaw manifests as improper handling of reference counts, creating potential for system instability and security exploitation. The vulnerability falls under the category of improper handling of reference counts, which is classified as CWE-466 in the Common Weakness Enumeration catalog. This type of vulnerability typically enables attackers to manipulate object lifecycles and can lead to various security implications including privilege escalation or denial of service conditions.
The technical implementation of this vulnerability occurs within the kernel's sysfs interface for network device queue management. When the kernel processes network device queue operations through these functions, it fails to properly maintain reference count integrity for kernel objects. This mishandling creates a scenario where objects may be prematurely freed or retained beyond their intended lifecycle, potentially allowing for use-after-free conditions or object reuse vulnerabilities. The flaw is particularly concerning because it operates within the core networking subsystem where kernel objects are frequently accessed and manipulated during normal network operations. Attackers could exploit this by triggering specific network device queue operations that would cause the reference counting mechanism to malfunction, potentially leading to memory corruption or arbitrary code execution in kernel space.
The operational impact of CVE-2019-20811 extends beyond simple system instability to potentially enable privilege escalation and system compromise. Systems running affected kernel versions are vulnerable to exploitation through network device queue manipulation attacks, which could be initiated remotely or locally. The vulnerability aligns with ATT&CK technique T1068 by potentially enabling local privilege escalation through kernel memory corruption. Organizations running Linux systems with kernel versions before 5.0.6 face significant risk as this flaw could be leveraged to gain elevated privileges or cause system crashes. The attack surface includes any system that utilizes network device queue management features, making it particularly relevant for servers, network appliances, and any infrastructure relying on kernel networking capabilities. The vulnerability's impact is amplified by the fact that it operates at the kernel level, where successful exploitation could result in complete system compromise.
Mitigation strategies for CVE-2019-20811 primarily focus on kernel version updates and system hardening measures. The most effective remediation involves upgrading to Linux kernel version 5.0.6 or later where the reference count handling has been corrected. System administrators should prioritize patching affected systems and implementing proper kernel version management policies to prevent similar vulnerabilities. Additional mitigations include monitoring network device queue operations and implementing kernel lockdown features where applicable. The vulnerability demonstrates the importance of proper reference counting in kernel space programming and highlights the need for thorough code review processes. Organizations should also consider implementing network segmentation and access controls to limit potential exploitation vectors. Security teams should monitor for exploitation attempts targeting this specific vulnerability and maintain updated threat intelligence on related kernel vulnerabilities. The fix for this issue represents a fundamental correction to kernel object lifecycle management, aligning with security best practices for kernel development and emphasizing the critical importance of proper memory management in operating system components.