# 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.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 26 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97733, BELL-CVE-2026-74748, DEBIAN-CVE-2026-74748, GHSA-hf83-xv8x-wgq9, UBUNTU-CVE-2026-74748

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74748 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-74748 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74748/ (Markdown: https://insights.sbomify.com/CVE-2026-74748/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74748
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74748
- OSV: https://osv.dev/vulnerability/CVE-2026-74748

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74748/
Summaries are generated and may contain mistakes; the official description above is the record.