# CVE-2026-81001: slip: fix use-after-free in sl_sync()

> A use-after-free vulnerability in the Linux kernel's SLIP driver allows local attackers to execute arbitrary code or escalate privileges via race conditions.

- **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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-81001, DEBIAN-CVE-2026-81001, GHSA-pxg4-rg6h-vm8p, UBUNTU-CVE-2026-81001

## What is CVE-2026-81001?

CVE-2026-81001 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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:

slip: fix use-after-free in sl_sync()

slip_devs[] stores bare net_device pointers and takes no reference on
them.  sl_sync() and sl_alloc() walk that table from slip_open() under
rtnl_lock(), while an entry is dropped by sl_free_netdev(), which
sl_setup() installs as dev->priv_destructor.

priv_destructor is called from netdev_run_todo(), which deliberately
runs with the RTNL semaphore released so that it can sleep while waiting
for the device refcount to drop:

	/* Snapshot list, allow later requests */
	list_replace_init(&net_todo_list, &list);

	__rtnl_unlock();
	...
		if (dev->priv_destructor)
			dev->priv_destructor(dev);	/* slip_devs[i] = NULL */
		if (dev->needs_free_netdev)
			free_netdev(dev);
		...
		/* Free network device */
		kobject_put(&dev->dev.kobj);

So rtnl_lock() does not serialise slip_open() against the teardown at
all.  sl_sync() can load slip_devs[i] while the entry is still published
and dereference it after netdev_run_todo() has run the destructor and
released the device:

  CPU0 (slip_open)                 CPU1 (slip_close)
                                   unregister_netdev()
                                     rtnl_unlock()
                                       netdev_run_todo()
                                         __rtnl_unlock()
  rtnl_lock()
  sl_sync()
    dev = slip_devs[i]
                                         priv_destructor(dev)
                                           slip_devs[i] = NULL
                                         kobject_put(&dev->dev.kobj)
                                           /* dev is freed */
    sl = netdev_priv(dev)
    if (sl->tty || sl->leased)     /* use-after-free */

  BUG: KASAN: use-after-free in sl_sync drivers/net/slip/slip.c:730 [inline]
  BUG: KASAN: use-after-free in slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806
  Read of size 1 at addr ffff8880712dac71 by task syz-executor.2/6506

  CPU: 2 PID: 6506 Comm: syz-executor.2 Not tainted 6.1.134-syzkaller-00260-g0c8fc3469765 #0
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
  Call Trace:
   sl_sync drivers/net/slip/slip.c:730 [inline]
   slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806
   tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433
   tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564
   tiocsetd drivers/tty/tty_io.c:2428 [inline]
   tty_ioctl+0x5f0/0x1530 drivers/tty/tty_io.c:2712

  Allocated by task 6502:
   alloc_netdev_mqs+0x98/0xfe0 net/core/dev.c:10719
   sl_alloc drivers/net/slip/slip.c:756 [inline]
   slip_open+0x36d/0x1210 drivers/net/slip/slip.c:817
   tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433
   tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564

  Freed by task 6497:
   device_release+0xa2/0x240 drivers/base/core.c:2507
   kobject_put+0x179/0x280 lib/kobject.c:729
   netdev_run_todo+0x6c8/0xef0 net/core/dev.c:10509
   slip_close+0x166/0x1c0 drivers/net/slip/slip.c:906
   tty_ldisc_close+0x113/0x1a0 drivers/tty/tty_ldisc.c:456
   tty_ldisc_kill+0x94/0x160 drivers/tty/tty_ldisc.c:614
   tty_ldisc_release+0xe3/0x2b0 drivers/tty/tty_ldisc.c:782
   tty_release+0xbcc/0xe70 drivers/tty/tty_io.c:1860

Commit e58c19124189 ("slip: Fix use-after-free Read in slip_open") fixed
a different source of stale entries - a device left in slip_devs[] after
slip_open() freed it on the registration error path - and does not
address this race, which is why the report survives it.

Drop the entry from ndo_uninit instead.  unregister_netdevice() calls
ndo_uninit under RTNL, before the device is queued to netdev_run_todo(),
so an entry that sl_sync() can still see while holding RTNL belongs to a
device that cannot be freed until RTNL is dropped.  sl_free_netdev()
stays only for the slip_open() error path, where register_netdevice()
may have failed before ndo_init and ndo_uninit is then not called
either.  Both running for the same device is harmless: the
---truncated---

## Which versions are affected by CVE-2026-81001?


## How do I fix CVE-2026-81001?

Apply the vendor's patch.

## Is CVE-2026-81001 being exploited?

There is no known exploitation of CVE-2026-81001 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81001 and fix it if it is affected.

What it is: CVE-2026-81001 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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-2026-81001 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-2026-81001/ (Markdown: https://insights.sbomify.com/CVE-2026-81001/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81001
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81001
- OSV: https://osv.dev/vulnerability/CVE-2026-81001

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81001/
Summaries are generated and may contain mistakes; the official description above is the record.