CVE-2026-64043 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
ovpn: fix race between deleting interface and adding new peer
While deleting an existing ovpn interface, there is a very narrow window where adding a new peer via netlink may cause the netdevice to hang and prevent its unregistration.
It may happen during ovpn_dellink(), when all existing peers are freed and the device is queued for deregistration, but a CMD_PEER_NEW message comes in adding a new peer that takes again a reference to the netdev.
At this point there is no way to release the device because we are under the assumption that all peers were already released.
Fix the race condition by releasing all peers in ndo_uninit(), when the netdevice has already been removed from the netdev list.
Also ovpn_peer_add() has now an extra check that forces the function to bail out if the device reg_state is not REGISTERED. This way any incoming CMD_PEER_NEW racing with the interface deletion routine will simply stop before adding the peer.
Note that the above check happens while holding the netdev_lock to prevent racing netdev state changes.
ovpn_dellink() is now empty and can be removed.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the Linux kernel's openvpn (ovpn) network driver implementation, specifically addressing a critical race condition that can lead to system instability and potential denial of service scenarios. The issue manifests during the interface deletion process where concurrent operations can cause unpredictable behavior in the network device management subsystem. When an ovpn interface is being removed through the ovpn_dellink() function, there exists a temporal window where new peer addition operations can interfere with the cleanup process, creating a deadlock scenario that prevents proper device unregistration.
The technical flaw stems from improper synchronization between the interface deletion routine and peer management operations within the network device framework. During ovpn_dellink() execution, all existing peers are freed and the netdevice is scheduled for deregistration, yet a CMD_PEER_NEW netlink message can arrive simultaneously to add a new peer. This race condition occurs because the system assumes all peers have been released when in reality a new peer reference can be established against the already queued-for-deletion netdevice, creating an impossible state where the device cannot be properly unregistered. The vulnerability represents a classic race condition scenario that violates proper resource management protocols and can result in system hang conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise system stability and network functionality. When the netdevice hangs due to this race condition, it prevents proper cleanup operations from completing, which can lead to memory leaks, resource exhaustion, and persistent network interface states that interfere with subsequent network operations. The vulnerability affects any system running Linux kernels with the affected openvpn driver implementation and can be exploited through malicious or legitimate netlink operations that trigger concurrent interface deletion and peer addition sequences.
The fix implements a comprehensive solution that addresses both the root cause and prevention mechanisms of this race condition. The primary approach involves moving peer release operations from the deletion context to the ndo_uninit() function, which executes after the netdevice has been removed from the network device list, ensuring proper cleanup ordering. Additionally, the ovpn_peer_add() function now includes a critical state check that verifies the device registration state before proceeding with peer addition operations. This validation occurs while holding the netdev_lock to prevent concurrent state changes that could bypass the protection mechanism.
The mitigation strategy also includes the removal of the empty ovpn_dellink() function, which eliminates potential confusion and ensures the cleanup process follows the proper kernel network device management patterns. This solution aligns with established security practices for managing concurrent access to shared resources and prevents the specific race condition described in the vulnerability. The implementation follows standard kernel development best practices and addresses the underlying CWE-362 (Concurrent Execution using Shared Resource with Unprotected Read-Write Access) pattern, which is categorized under the ATT&CK technique T1499.004 (Evasion: Virtualization/Sandbox Evasion) when considering system stability threats.
The fix ensures that device state transitions are properly synchronized and that network device cleanup operations complete successfully even under concurrent access conditions. By enforcing proper state validation during peer addition operations and reorganizing the cleanup sequence, the vulnerability is resolved without compromising the functionality of the openvpn driver. This approach maintains backward compatibility while eliminating the race condition through proper locking mechanisms and execution ordering, making it suitable for deployment in production environments where network reliability and system stability are critical requirements.