# CVE-2026-74264: net: watchdog: fix refcount tracking races

> A race condition in the Linux kernel network watchdog allows concurrent access to reference tracking data, causing list corruption and system crashes.

- **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:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-96027, BELL-CVE-2026-74264, DEBIAN-CVE-2026-74264, GHSA-6cq5-2879-x586, UBUNTU-CVE-2026-74264

## What is CVE-2026-74264?

CVE-2026-74264 is a high-severity vulnerability in Linux, published on 15 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:

net: watchdog: fix refcount tracking races

Blamed commit converted the untracked dev_hold()/dev_put() calls
in the watchdog code to use the tracked dev_hold_track()/dev_put_track()
(which were later renamed/interfaced to netdev_hold() and netdev_put()).

By introducing dev->watchdog_dev_tracker to store the
reference tracking information without adding synchronization
between netdev_watchdog_up() and dev_watchdog(), it enabled the
race condition where this pointer could be overwritten or freed
concurrently, leading to the list corruption crash syzbot reported:

list_del corruption, ffff888114a18c00->next is NULL
 kernel BUG at lib/list_debug.c:52 !
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 91 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound linkwatch_event
 RIP: 0010:__list_del_entry_valid_or_report.cold+0x22/0x2a lib/list_debug.c:52
Call Trace:
 <TASK>
  __list_del_entry_valid include/linux/list.h:132 [inline]
  __list_del_entry include/linux/list.h:246 [inline]
  list_move_tail include/linux/list.h:341 [inline]
  ref_tracker_free+0x1a7/0x6c0 lib/ref_tracker.c:329
  netdev_tracker_free include/linux/netdevice.h:4491 [inline]
  netdev_put include/linux/netdevice.h:4508 [inline]
  netdev_put include/linux/netdevice.h:4504 [inline]
  netdev_watchdog_down net/sched/sch_generic.c:600 [inline]
  dev_deactivate_many+0x28c/0xfe0 net/sched/sch_generic.c:1363
  dev_deactivate+0x109/0x1d0 net/sched/sch_generic.c:1397
  linkwatch_do_dev net/core/link_watch.c:184 [inline]
  linkwatch_do_dev+0xd3/0x120 net/core/link_watch.c:166
  __linkwatch_run_queue+0x3a5/0x810 net/core/link_watch.c:240
  linkwatch_event+0x8f/0xc0 net/core/link_watch.c:314
  process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
  process_scheduled_works kernel/workqueue.c:3397 [inline]
  worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
  kthread+0x370/0x450 kernel/kthread.c:436
  ret_from_fork+0x69a/0xc80 arch/x86/kernel/process.c:158
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

This patch has three coordinated parts:

1) Add dev->watchdog_lock and dev->watchdog_ref_held to serialize watchdog operations.

2) Remove netdev_watchdog_up() call from netif_carrier_on():
   This ensures netdev_watchdog_up() is only called from process/BH context
   (via linkwatch workqueue dev_activate()), allowing us to use
   spin_lock_bh() for synchronization.

3) Synchronize watchdog up and watchdog timer:
   Protect netdev_watchdog_up() with tx_global_lock and watchdog_lock.
   Only allocate a new tracker in netdev_watchdog_up() if one is
   not already present.
   In dev_watchdog(), ensure we don't release the tracker if the
   timer was rescheduled either by dev_watchdog() itself or concurrently
   by netdev_watchdog_up().

## Which versions are affected by CVE-2026-74264?


## How do I fix CVE-2026-74264?

Apply the vendor's patch.

## Is CVE-2026-74264 being exploited?

There is no known exploitation of CVE-2026-74264 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74264 and fix it if it is affected.

What it is: CVE-2026-74264 is a high-severity vulnerability in Linux, published on 15 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-2026-74264 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-2026-74264/ (Markdown: https://insights.sbomify.com/CVE-2026-74264/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74264
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74264
- OSV: https://osv.dev/vulnerability/CVE-2026-74264

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74264/
Summaries are generated and may contain mistakes; the official description above is the record.