# CVE-2026-23273: macvlan: observe an RCU grace period in macvlan_common_newlink() error path

> A race condition in the Linux kernel macvlan driver allows a use-after-free, potentially leading to code execution or system crash.

- **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:** 20 Mar 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-23273, DEBIAN-CVE-2026-23273, GHSA-r5gh-q6f7-7q3v, ROOT-OS-DEBIAN-11-CVE-2026-23273, ROOT-OS-DEBIAN-12-CVE-2026-23273, ROOT-OS-DEBIAN-13-CVE-2026-23273, ROOT-OS-UBUNTU-2204-CVE-2026-23273, ROOT-OS-UBUNTU-2404-CVE-2026-23273

## What is CVE-2026-23273?

CVE-2026-23273 is a high-severity use after free vulnerability in Linux kernel, published on 20 Mar 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:

macvlan: observe an RCU grace period in macvlan_common_newlink() error path

valis reported that a race condition still happens after my prior patch.

macvlan_common_newlink() might have made @dev visible before
detecting an error, and its caller will directly call free_netdev(dev).

We must respect an RCU period, either in macvlan or the core networking
stack.

After adding a temporary mdelay(1000) in macvlan_forward_source_one()
to open the race window, valis repro was:

ip link add p1 type veth peer p2
ip link set address 00:00:00:00:00:20 dev p1
ip link set up dev p1
ip link set up dev p2
ip link add mv0 link p2 type macvlan mode source

(ip link add invalid% link p2 type macvlan mode source macaddr add
00:00:00:00:00:20 &) ; sleep 0.5 ; ping -c1 -I p1 1.2.3.4
PING 1.2.3.4 (1.2.3.4): 56 data bytes
RTNETLINK answers: Invalid argument

BUG: KASAN: slab-use-after-free in macvlan_forward_source
(drivers/net/macvlan.c:408 drivers/net/macvlan.c:444)
Read of size 8 at addr ffff888016bb89c0 by task e/175

CPU: 1 UID: 1000 PID: 175 Comm: e Not tainted 6.19.0-rc8+ #33 NONE
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
Call Trace:
<IRQ>
dump_stack_lvl (lib/dump_stack.c:123)
print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
? macvlan_forward_source (drivers/net/macvlan.c:408 drivers/net/macvlan.c:444)
kasan_report (mm/kasan/report.c:597)
? macvlan_forward_source (drivers/net/macvlan.c:408 drivers/net/macvlan.c:444)
macvlan_forward_source (drivers/net/macvlan.c:408 drivers/net/macvlan.c:444)
? tasklet_init (kernel/softirq.c:983)
macvlan_handle_frame (drivers/net/macvlan.c:501)

Allocated by task 169:
kasan_save_stack (mm/kasan/common.c:58)
kasan_save_track (./arch/x86/include/asm/current.h:25
mm/kasan/common.c:70 mm/kasan/common.c:79)
__kasan_kmalloc (mm/kasan/common.c:419)
__kvmalloc_node_noprof (./include/linux/kasan.h:263 mm/slub.c:5657
mm/slub.c:7140)
alloc_netdev_mqs (net/core/dev.c:12012)
rtnl_create_link (net/core/rtnetlink.c:3648)
rtnl_newlink (net/core/rtnetlink.c:3830 net/core/rtnetlink.c:3957
net/core/rtnetlink.c:4072)
rtnetlink_rcv_msg (net/core/rtnetlink.c:6958)
netlink_rcv_skb (net/netlink/af_netlink.c:2550)
netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)
netlink_sendmsg (net/netlink/af_netlink.c:1894)
__sys_sendto (net/socket.c:727 net/socket.c:742 net/socket.c:2206)
__x64_sys_sendto (net/socket.c:2209)
do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:131)

Freed by task 169:
kasan_save_stack (mm/kasan/common.c:58)
kasan_save_track (./arch/x86/include/asm/current.h:25
mm/kasan/common.c:70 mm/kasan/common.c:79)
kasan_save_free_info (mm/kasan/generic.c:587)
__kasan_slab_free (mm/kasan/common.c:287)
kfree (mm/slub.c:6674 mm/slub.c:6882)
rtnl_newlink (net/core/rtnetlink.c:3845 net/core/rtnetlink.c:3957
net/core/rtnetlink.c:4072)
rtnetlink_rcv_msg (net/core/rtnetlink.c:6958)
netlink_rcv_skb (net/netlink/af_netlink.c:2550)
netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344)
netlink_sendmsg (net/netlink/af_netlink.c:1894)
__sys_sendto (net/socket.c:727 net/socket.c:742 net/socket.c:2206)
__x64_sys_sendto (net/socket.c:2209)
do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:131)

Weakness: CWE-416 (Use After Free), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-23273?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23273?

Apply the vendor's patch.

## Is CVE-2026-23273 being exploited?

There is no known exploitation of CVE-2026-23273 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23273 and fix it if it is affected.

What it is: CVE-2026-23273 is a high-severity use after free vulnerability in Linux kernel, published on 20 Mar 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-2026-23273 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-23273/ (Markdown: https://insights.sbomify.com/CVE-2026-23273/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23273
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23273
- OSV: https://osv.dev/vulnerability/CVE-2026-23273

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23273/
Summaries are generated and may contain mistakes; the official description above is the record.