CVE-2022-49672 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
net: tun: unlink NAPI from device on destruction
Syzbot found a race between tun file and device destruction. NAPIs live in struct tun_file which can get destroyed before the netdev so we have to del them explicitly. The current code is missing deleting the NAPI if the queue was detached first.
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Analysis
by VulDB Data Team • 10/24/2025
The vulnerability identified as CVE-2022-49672 represents a critical race condition within the Linux kernel's TUN (Tunnel) network driver implementation that can lead to system instability and potential security implications. This issue specifically affects the interaction between the TUN network interface and the Network API (NAPI) framework, where improper synchronization during device destruction creates opportunities for memory corruption and system crashes. The vulnerability was discovered through automated fuzzing by syzbot, which systematically tests kernel code paths to identify potential race conditions and memory safety issues. The TUN driver is commonly used for creating virtual network interfaces that enable applications to send and receive network packets through software interfaces, making it a critical component in various networking scenarios including VPN implementations, container networking, and network testing environments.
The technical flaw manifests in the improper handling of NAPI structures during the destruction sequence of TUN network devices. In the Linux kernel's networking subsystem, NAPI (Network API) is a framework designed to optimize network packet processing by allowing drivers to defer processing until a certain threshold is reached, thereby improving system performance. However, the vulnerability occurs because NAPI structures are embedded within the tun_file structure, which can be destroyed before the associated network device structure. When a TUN device is destroyed, the code fails to explicitly unlink the NAPI from the network device if the queue has already been detached, creating a dangling reference scenario. This race condition can result in memory being accessed after it has been freed, leading to kernel oops, system crashes, or potentially exploitable memory corruption conditions. The issue is particularly concerning because it involves the destruction sequence of network interfaces, which can be triggered by various legitimate operations including network configuration changes, application termination, or system maintenance activities.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise the stability and security of systems relying on TUN interfaces for network operations. When the race condition occurs, the kernel may experience unpredictable behavior ranging from immediate system panics to more subtle memory corruption that could be exploited by malicious actors. Systems using TUN interfaces for VPN services, container networking, or network virtualization are particularly at risk since these environments frequently create and destroy network interfaces. The vulnerability can be triggered through normal network interface operations, making it difficult to predict or prevent in production environments. The attack surface is broad as any application or system component that utilizes TUN network interfaces could potentially expose the system to this race condition, including network management tools, virtualization platforms, and security applications that rely on TUN interfaces for their operation.
Mitigation strategies for CVE-2022-49672 focus on ensuring proper synchronization and explicit cleanup of NAPI structures during device destruction sequences. The fix implemented in the kernel involves explicitly unlinking NAPI structures from network devices before allowing the tun_file structure to be destroyed, thereby preventing the race condition that leads to dangling references. System administrators should ensure their systems are updated with kernel versions containing the patched code, which typically involves applying the relevant security patches from the Linux kernel stable releases. Organizations using TUN interfaces extensively should implement monitoring for kernel oops messages or system crashes that could indicate the presence of this vulnerability. The mitigation aligns with best practices for kernel security and follows principles outlined in the Common Weakness Enumeration (CWE) category CWE-362, which addresses race conditions in concurrent systems. From an ATT&CK framework perspective, this vulnerability relates to privilege escalation and denial of service techniques that could be leveraged by adversaries to destabilize systems or potentially gain unauthorized access to network resources through manipulation of network interface management operations. Regular kernel updates and security audits of network interface usage patterns are recommended to prevent exploitation of similar race condition vulnerabilities in the broader kernel networking subsystem.