CVE-2026-68338 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
net/packet: avoid fanout hook re-registration after unregister
packet_set_ring() temporarily detaches a socket from packet delivery while reconfiguring its ring. It records the previous running state, clears po->num, unregisters the protocol hook when needed, drops po->bind_lock, and later restores po->num and re-registers the hook from the saved was_running value.
That unlocked window can race with NETDEV_UNREGISTER. The notifier can observe the socket as not running, skip __unregister_prot_hook(), and invalidate the per-socket binding by setting po->ifindex to -1 and clearing po->prot_hook.dev. A one-member fanout group can still retain its shared fanout hook device pointer. When packet_set_ring() resumes, re-registering solely from the stale was_running state can re-add the fanout hook after the device has been unregistered.
Treat po->ifindex == -1 as an invalidated binding after reacquiring po->bind_lock. This is distinct from ifindex 0, the normal unbound/wildcard state: ifindex -1 marks an existing device binding that was invalidated when the device was unregistered. Restore po->num as before, but do not re-register the hook if device unregister already detached the socket.
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Analysis
by VulDB Data Team • 08/11/2026
This vulnerability exists in the linux kernel's packet socket implementation within the net/packet subsystem where a race condition can occur during ring configuration operations. The flaw manifests when packet_set_ring() function temporarily detaches a socket from packet delivery while reconfiguring its ring buffer. During this process, the function records the previous running state, clears the socket's num field, unregisters the protocol hook when necessary, releases the bind_lock, and later restores the num field while re-registering the hook based on the saved was_running value. This sequence creates an unlocked window where concurrent operations can interfere with the normal socket lifecycle management.
The race condition specifically occurs between the packet_set_ring() operation and the NETDEV_UNREGISTER notification handler. When a network device is being unregistered, the notifier observes the socket in a state where it appears not running, causing it to skip the __unregister_prot_hook() function call. This invalidates the per-socket binding by setting po->ifindex to -1 and clearing the po->prot_hook.dev pointer. The vulnerability becomes particularly problematic when dealing with one-member fanout groups that maintain shared fanout hook device pointers. When packet_set_ring() resumes its operation, it attempts to re-register the hook solely based on the stale was_running state, which can inadvertently add a fanout hook after the device has already been unregistered.
This particular vulnerability aligns with CWE-362, which describes a race condition in concurrent programming where operations are not properly synchronized. The issue also maps to ATT&CK technique T1059.007 for system service manipulation and T1566 for phishing attacks that could exploit the instability of network socket handling. The root cause stems from inadequate state validation during socket reconfiguration, where the system fails to properly account for device unregistration events that occur during the temporary socket detachment period.
The operational impact of this vulnerability extends beyond simple socket management issues and can potentially lead to system instability and security concerns. An attacker could exploit this race condition to create inconsistent network socket states that might allow for privilege escalation or denial of service attacks. The invalidation of device bindings through ifindex -1 creates a scenario where the kernel maintains references to devices that no longer exist, potentially leading to memory corruption or improper packet delivery behavior.
The fix implemented addresses this by treating po->ifindex == -1 as an invalidated binding after reacquiring the po->bind_lock, distinguishing it from the normal unbound/wildcard state of ifindex 0. This change ensures that when a socket's device binding has been invalidated due to device unregistration, the system properly recognizes this condition and avoids attempting to re-register hooks on non-existent devices. The solution maintains the existing behavior of restoring po->num but prevents the problematic hook re-registration that could occur with stale state information, effectively closing the race condition window while preserving legitimate socket functionality.
This vulnerability represents a classic example of improper synchronization in kernel-level code where temporal dependencies between system operations create exploitable conditions. The fix demonstrates proper defensive programming by validating socket binding states before attempting protocol hook operations, preventing potential use-after-free scenarios and maintaining kernel stability during concurrent device management operations. The resolution aligns with best practices for kernel security by ensuring that all state transitions are properly validated and that references to potentially invalidated resources are properly handled before system resources are reacquired or modified.