CVE-2026-74718 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
devlink: fix net namespace reference leak in reload
devlink_nl_reload_doit() calls devlink_netns_get(), which returns a net with a held reference. When the requested namespace differs from the current one and the reload action is not DRIVER_REINIT, the function returns -EOPNOTSUPP without releasing the reference. Add the missing put_net() on this error path.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel devlink subsystem manages device configuration and state through a netlink interface that allows user-space applications to interact with network devices. A critical resource management flaw was identified within the reload command handler, specifically in the function devlink_nl_reload_doit(). This vulnerability stems from an improper handling of reference counts for network namespaces when performing administrative operations on hardware drivers. The core issue arises during the execution flow where a request is made to reload a device configuration or state across different network namespace boundaries.
When a user initiates a reload operation that targets a netlink socket associated with a specific network namespace, the kernel invokes devlink_netns_get() to acquire and increment the reference count for that target namespace. This mechanism ensures that the namespace object remains valid throughout the duration of the operation. However, under certain conditions where the requested network namespace differs from the current execution context's namespace, and the reload action type is not classified as DRIVER_REINIT, the function encounters a logic path that returns an error code indicating unsupported operation (-EOPNOTSUPP). In this specific scenario, the previously acquired reference to the target network namespace was never released.
This omission results in a persistent net namespace reference leak. Because the kernel maintains a global list of active namespaces and tracks their usage counts via atomic variables, failing to call put_net() on the error path means that the reference count for the targeted namespace remains artificially elevated. Over time, as administrators or automated systems issue repeated reload commands targeting different non-current namespaces without triggering driver reinitialization, these unreleased references accumulate. This accumulation prevents the kernel from properly cleaning up and destroying network namespaces when they are no longer in use by any processes.
The operational impact of this vulnerability is primarily a denial-of-service condition through resource exhaustion. As the number of leaked namespace references grows, it consumes kernel memory resources associated with each active namespace structure. In severe cases, particularly on systems running many containers or virtualized network environments where frequent cross-namespace operations are common, this leak can lead to system instability. Eventually, the inability to reclaim these namespaces may contribute to overall resource pressure, potentially affecting other subsystems that rely on available kernel memory for allocation. While not directly exploitable for privilege escalation in most standard configurations, it represents a significant reliability issue for long-running systems with dynamic network topology changes.
From a classification perspective, this vulnerability aligns with CWE-401, which describes the failure to release a resource after its use is complete or when an error occurs. The specific mechanism involves missing cleanup code on an exceptional execution path within a system call handler. In terms of attack patterns, while not directly mapped to a single ATT&CK technique due to its nature as a bug rather than an exploit vector, it relates to the broader category of resource exhaustion attacks where adversaries might attempt to degrade service availability by triggering repeated error conditions that leak kernel resources.
The resolution involves modifying the devlink_nl_reload_doit() function in the Linux kernel source code to ensure proper reference counting hygiene. Specifically, a call to put_net() is added immediately before returning -EOPNOTSUPP on the affected error path. This change guarantees that any network namespace acquired via devlink_netns_get() is correctly dereferenced and released, regardless of whether the operation succeeds or fails due to unsupported action types across namespaces. Developers should apply this patch in their kernel builds to prevent gradual resource degradation. System administrators monitoring for unusual memory growth patterns related to net_namespace structures may find this fix essential for maintaining stability in complex networked environments.