CVE-2026-74748 netfilter: ipset: fix refcount race between list:set GC and swap
A race condition in Linux kernel ipset allows local attackers to trigger a kernel panic and denial of service via concurrent garbage collection and swap operations.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74748?
CVE-2026-74748 is a high-severity vulnerability in Linux, published on 26 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
netfilter: ipset: fix refcount race between list:set GC and swap
__ip_set_put_byindex() resolved the index to a set pointer under RCU, then took ip_set_ref_lock in __ip_set_put() to decrement set->ref. ip_set_swap() holds that same lock while swapping both the ip_set_list slots and the two sets' ref counters, so it can interleave between the dereference and the lock acquisition, leaving the caller to decrement a set whose reference already moved to the other index and hit BUG_ON(set->ref == 0). list_set_gc() reaches this from timer softirq, which the nfnl mutex does not serialize against swap: an expiring list:set member calls list_set_del() -> ip_set_put_byindex() while IPSET_CMD_SWAP runs on the referenced sets.
Resolve the index and decrement under ip_set_ref_lock, as ip_set_swap() already does, keeping the refcount tied to the index rather than to a stale set pointer.
kernel BUG at net/netfilter/ipset/ip_set_core.c:685! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:ip_set_put_byindex (net/netfilter/ipset/ip_set_core.c:870) Call Trace: <IRQ> list_set_del (net/netfilter/ipset/ip_set_list_set.c:159) set_cleanup_entries (net/netfilter/ipset/ip_set_list_set.c:181) list_set_gc (net/netfilter/ipset/ip_set_list_set.c:578) call_timer_fn (kernel/time/timer.c:1748) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2374) run_timer_softirq (kernel/time/timer.c:2405) </IRQ> Kernel panic - not syncing: Fatal exception in interrupt
Which versions are affected by CVE-2026-74748?
How do I fix CVE-2026-74748?
Apply the vendor's patch.
Is CVE-2026-74748 being exploited?
There is no known exploitation of CVE-2026-74748 in the wild and no public exploit code.
Sources
Also known as AZL-97733, BELL-CVE-2026-74748, DEBIAN-CVE-2026-74748, GHSA-hf83-xv8x-wgq9, UBUNTU-CVE-2026-74748.