Bug 2468172 (CVE-2026-43374)

Summary: CVE-2026-43374 kernel: net: nexthop: fix percpu use-after-free in remove_nh_grp_entry
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's networking (net: nexthop) component. When a nexthop is removed from a group, the system prematurely frees per-CPU (percpu) statistics memory. This timing issue allows other parts of the kernel that are still referencing the old group to access and potentially corrupt the freed memory. This use-after-free vulnerability can lead to system instability or a denial of service.
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Description OSIDB Bzimport 2026-05-08 15:02:56 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: nexthop: fix percpu use-after-free in remove_nh_grp_entry

When removing a nexthop from a group, remove_nh_grp_entry() publishes
the new group via rcu_assign_pointer() then immediately frees the
removed entry's percpu stats with free_percpu(). However, the
synchronize_net() grace period in the caller remove_nexthop_from_groups()
runs after the free. RCU readers that entered before the publish still
see the old group and can dereference the freed stats via
nh_grp_entry_stats_inc() -> get_cpu_ptr(nhge->stats), causing a
use-after-free on percpu memory.

Fix by deferring the free_percpu() until after synchronize_net() in the
caller. Removed entries are chained via nh_list onto a local deferred
free list. After the grace period completes and all RCU readers have
finished, the percpu stats are safely freed.
Comment 1 Keith Grant 2026-05-08 21:01:58 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050830-CVE-2026-43374-385e@gregkh/T