Infinite Loop Vulnerability in Open vSwitch due to Device Unregistration in Linux Kernel
Summary
CVE-2025-21681: In the Linux kernel, the following vulnerability has been resolved: openvswitch: fix lockup on tx to unregistering netdev with carrier Commit in a fixes tag attempted to fix the issue in the following sequence of calls:... Affects linux versions < 6.1.128-1. Fixed in 6.1.128-1. How to fix ↓
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Background
The Linux kernel is a core component of the operating system that manages hardware and system resources. It provides essential services for all other parts of the operating system, including process management, memory management, and device control. Open vSwitch (OVS) is a multilayer virtual switch designed to enable network automation while supporting standard management interfaces and protocols. This vulnerability affects the OVS component when interacting with network devices that are in the process of unregistering, leading to potential system lockups.
Vulnerability Detail
The vulnerability arises from an infinite loop in the skb_tx_hash function when a network device is unregistering. During this process, the device's real_num_tx_queues is set to zero, causing the loop condition to always evaluate to true. This can lead to a system lockup, as the core becomes unresponsive. The issue is exacerbated by certain devices, like net/dummy, which may report an active carrier status even while unregistering, leading to further complications. The vulnerability can affect network performance and stability, necessitating immediate attention.
How To Fix
Minimum fixed version
6.1.128-1
This is the first release that contains the fix.
sudo apt-get install --only-upgrade linuxTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, users can avoid using network devices that are known to cause this issue while they are in the process of unregistering. Additionally, monitoring the device states and ensuring they are not in the unregistering phase before attempting to transmit packets can help mitigate the risk of encountering the infinite loop.
Conclusion
The CVE-2025-21681 vulnerability poses a significant risk to systems using the Linux kernel and Open vSwitch, particularly during the unregistering of network devices. Immediate action is recommended to update the kernel to the patched version to prevent potential system lockups. Users should also consider temporary workarounds until they can apply the necessary updates.
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FAQ
CVE-2025-21681 is a vulnerability in the Linux kernel that causes an infinite loop in the Open vSwitch when a network device is unregistering.
This vulnerability can lead to system lockups, making the kernel unresponsive and potentially requiring a reboot to recover.
Yes, users are advised to update their Linux kernel to the latest version that includes the fix for CVE-2025-21681.
As a temporary measure, avoid using network devices that may cause this issue during their unregistering phase.
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