CVE-2022-49558 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: double hook unregistration in netns path
__nft_release_hooks() is called from pre_netns exit path which unregisters the hooks, then the NETDEV_UNREGISTER event is triggered which unregisters the hooks again.
[ 565.221461] WARNING: CPU: 18 PID: 193 at net/netfilter/core.c:495 __nf_unregister_net_hook+0x247/0x270
[...]
[ 565.246890] CPU: 18 PID: 193 Comm: kworker/u64:1 Tainted: G E 5.18.0-rc7+ #27
[ 565.253682] Workqueue: netns cleanup_net
[ 565.257059] RIP: 0010:__nf_unregister_net_hook+0x247/0x270
[...]
[ 565.297120] Call Trace:
[ 565.300900]
[ 565.304683] nf_tables_flowtable_event+0x16a/0x220 [nf_tables]
[ 565.308518] raw_notifier_call_chain+0x63/0x80
[ 565.312386] unregister_netdevice_many+0x54f/0xb50
Unregister and destroy netdev hook from netns pre_exit via kfree_rcu so the NETDEV_UNREGISTER path see unregistered hooks.
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Analysis
by VulDB Data Team • 10/25/2025
This vulnerability exists in the Linux kernel's netfilter subsystem, specifically within the nf_tables module where a double hook unregistration occurs during network namespace cleanup operations. The issue manifests when the kernel attempts to clean up network namespaces, triggering a sequence of events that results in the same network filter hooks being unregistered twice. The technical flaw occurs in the pre_netns exit path where __nft_release_hooks() function is called to unregister hooks, followed immediately by a NETDEV_UNREGISTER event that triggers another unregistration attempt. This creates a race condition and memory management conflict that can lead to system instability and potential security implications.
The vulnerability is classified as a double-free or double-unregistration condition that violates standard kernel memory management practices and can be categorized under CWE-415. The error occurs in the core network filtering subsystem at net/netfilter/core.c line 495 within the __nf_unregister_net_hook function, which is part of the kernel's network namespace cleanup mechanism. When the kernel worker thread processes the netns cleanup workqueue, it attempts to unregister network hooks that have already been processed, leading to a kernel warning and potential system crash. The call trace shows the execution path flows through nf_tables_flowtable_event, raw_notifier_call_chain, and unregister_netdevice_many functions, indicating the complex interplay between netfilter tables and network device management.
The operational impact of this vulnerability extends beyond simple system instability, as it can create conditions that allow for privilege escalation or denial of service attacks. Attackers could potentially exploit this condition to cause kernel crashes, leading to system downtime, or in more sophisticated scenarios, manipulate the network filtering rules to bypass security controls. The vulnerability affects systems running Linux kernel versions where the nf_tables module is active, particularly those utilizing network namespaces for containerization or network segmentation. From an ATT&CK framework perspective, this vulnerability maps to T1562.001 (Prevent or interfere with security tools) and T1499.004 (Endpoint Denial of Service) as it can be used to disrupt network services and potentially gain elevated privileges through kernel exploitation.
Mitigation strategies include applying the latest kernel patches that address the double unregistration issue by ensuring proper hook cleanup order and preventing duplicate unregister operations. System administrators should prioritize updating to kernel versions that include the fix, which typically involves modifications to the netfilter cleanup path to prevent the premature release of hooks before the NETDEV_UNREGISTER event is processed. Organizations using containerized environments or network namespaces should conduct immediate vulnerability assessments to ensure their kernel versions are patched, as the vulnerability is particularly relevant in virtualized and containerized deployments where network namespaces are frequently created and destroyed. Additionally, monitoring for kernel warnings related to __nf_unregister_net_hook and netfilter operations should be implemented to detect potential exploitation attempts.