# CVE-2026-90232: amt: Don't support cross-netns setup.

> A local attacker with high privileges can cause a kernel denial of service by triggering a bug in the Automatic Multicast Tunneling driver during cross-network namespace device unregistration.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102206, BELL-CVE-2026-90232, DEBIAN-CVE-2026-90232, GHSA-7h9j-j2h3-3xhw, UBUNTU-CVE-2026-90232

## What is CVE-2026-90232?

CVE-2026-90232 is a denial of service vulnerability in Linux, published on 17 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:

amt: Don't support cross-netns setup.

When a lower device is unregistered, amt_device_event() tries
to unregister its upper AMT device, but it has two problems.

  1. amt_lookup_upper_dev() looks up an upper device in the
      lower device's netns only

  2. amt_device_event() unregisters a single upper device only

If AMT device is created on a lower device in another netns,
removing the lower device triggers the splat below and gets
stuck until all upper devices are removed. [0]

The cross-netns setup seems unintentional considering 1. and
the following points:

  * amt_link_setup() sets dev->netns_immutable to true
  * skb_scrub_packet() is not called in the fast path
  * iproute2 binary fails to find cross-netns lower device via
    link-netns:
      # ip -n ns1 link add amt0 link-netns ns2 type amt dev veth1
      Cannot find device "veth1"

Instead of supporting it properly and preparing for per-netns
netdev unreg, let's forbid cross-netns setup.

Note that the problem 2. needs a separate fix.

[0]:
WARNING: net/core/dev.c:12518 at unregister_netdevice_many_notify+0x1cce/0x2250, CPU#48: ip/2031
Modules linked in:
CPU: 48 UID: 0 PID: 2031 Comm: ip Not tainted 7.2.0-rc5+ #27 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
RIP: 0010:unregister_netdevice_many_notify (net/core/dev.c:12518)
Code: 89 ef e8 d5 52 ae fe e9 d0 f4 ff ff 48 8d 3d f9 3b 9c 02 48 c7 c6 c0 0b 63 84 ba ab 1f 00 00 67 48 0f b9 3a e9 65 ff ff ff 90 <0f> 0b 90 eb 81 48 8d 3d f6 3b 9c 02 48 c7 c6 c0 0b 63 84 ba e2 1f
RSP: 0018:ffffc90004abf160 EFLAGS: 00010212
RAX: ffff888104d38260 RBX: ffff88800b0911b8 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff85b9f880
RBP: ffffc90004abf2d0 R08: ffffffff85b9f887 R09: 1ffffffff0b73f10
R10: dffffc0000000000 R11: fffffbfff0b73f11 R12: ffff88800b091d08
R13: ffff88800b091178 R14: dffffc0000000000 R15: ffff88800b091000
FS:  00007f555b86c600(0000) GS:ffff8881942a0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000562107d489c0 CR3: 0000000109a40002 CR4: 0000000000372ef0
Call Trace:
 <TASK>
 rtnl_dellink (net/core/rtnetlink.c:3632 net/core/rtnetlink.c:3674)
 rtnetlink_rcv_msg (net/core/rtnetlink.c:7112)
 netlink_rcv_skb (net/netlink/af_netlink.c:2556)
 netlink_unicast (net/netlink/af_netlink.c:1319)
 netlink_sendmsg (net/netlink/af_netlink.c:1900)
 ____sys_sendmsg (net/socket.c:775)
 __sys_sendmsg (net/socket.c:2738)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
...
unregister_netdevice: waiting for veth0 to become free. Usage count = 7
ref_tracker: netdev@ffff88800d7496d8 has 3/3 users at
     __netdev_adjacent_dev_insert (./include/linux/netdevice.h:4525 ./include/linux/netdevice.h:4554 net/core/dev.c:8791)
     __netdev_upper_dev_link (net/core/dev.c:8879 net/core/dev.c:8963)
     netdev_upper_dev_link (net/core/dev.c:9009)
     amt_newlink (drivers/net/amt.c:3321)

## Which versions are affected by CVE-2026-90232?


## How do I fix CVE-2026-90232?

Apply the vendor's patch.

## Is CVE-2026-90232 being exploited?

There is no known exploitation of CVE-2026-90232 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90232 and fix it if it is affected.

What it is: CVE-2026-90232 is a denial of service vulnerability in Linux, published on 17 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-2026-90232 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-2026-90232/ (Markdown: https://insights.sbomify.com/CVE-2026-90232/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90232
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90232
- OSV: https://osv.dev/vulnerability/CVE-2026-90232

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90232/
Summaries are generated and may contain mistakes; the official description above is the record.