# CVE-2025-21678: gtp: Destroy device along with udp socket's netns dismantle.

> A use-after-free vulnerability in the Linux kernel GTP module allows local attackers to cause a system crash by deleting network namespaces.

- **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:** 31 Jan 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-21678, DEBIAN-CVE-2025-21678, GHSA-52qf-338q-xphv, UBUNTU-CVE-2025-21678

## What is CVE-2025-21678?

CVE-2025-21678 is a high-severity use after free vulnerability in Linux kernel, published on 31 Jan 2025. 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:

gtp: Destroy device along with udp socket's netns dismantle.

gtp_newlink() links the device to a list in dev_net(dev) instead of
src_net, where a udp tunnel socket is created.

Even when src_net is removed, the device stays alive on dev_net(dev).
Then, removing src_net triggers the splat below. [0]

In this example, gtp0 is created in ns2, and the udp socket is created
in ns1.

  ip netns add ns1
  ip netns add ns2
  ip -n ns1 link add netns ns2 name gtp0 type gtp role sgsn
  ip netns del ns1

Let's link the device to the socket's netns instead.

Now, gtp_net_exit_batch_rtnl() needs another netdev iteration to remove
all gtp devices in the netns.

[0]:
ref_tracker: net notrefcnt@000000003d6e7d05 has 1/2 users at
     sk_alloc (./include/net/net_namespace.h:345 net/core/sock.c:2236)
     inet_create (net/ipv4/af_inet.c:326 net/ipv4/af_inet.c:252)
     __sock_create (net/socket.c:1558)
     udp_sock_create4 (net/ipv4/udp_tunnel_core.c:18)
     gtp_create_sock (./include/net/udp_tunnel.h:59 drivers/net/gtp.c:1423)
     gtp_create_sockets (drivers/net/gtp.c:1447)
     gtp_newlink (drivers/net/gtp.c:1507)
     rtnl_newlink (net/core/rtnetlink.c:3786 net/core/rtnetlink.c:3897 net/core/rtnetlink.c:4012)
     rtnetlink_rcv_msg (net/core/rtnetlink.c:6922)
     netlink_rcv_skb (net/netlink/af_netlink.c:2542)
     netlink_unicast (net/netlink/af_netlink.c:1321 net/netlink/af_netlink.c:1347)
     netlink_sendmsg (net/netlink/af_netlink.c:1891)
     ____sys_sendmsg (net/socket.c:711 net/socket.c:726 net/socket.c:2583)
     ___sys_sendmsg (net/socket.c:2639)
     __sys_sendmsg (net/socket.c:2669)
     do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)

WARNING: CPU: 1 PID: 60 at lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179)
Modules linked in:
CPU: 1 UID: 0 PID: 60 Comm: kworker/u16:2 Not tainted 6.13.0-rc5-00147-g4c1224501e9d #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Workqueue: netns cleanup_net
RIP: 0010:ref_tracker_dir_exit (lib/ref_tracker.c:179)
Code: 00 00 00 fc ff df 4d 8b 26 49 bd 00 01 00 00 00 00 ad de 4c 39 f5 0f 85 df 00 00 00 48 8b 74 24 08 48 89 df e8 a5 cc 12 02 90 <0f> 0b 90 48 8d 6b 44 be 04 00 00 00 48 89 ef e8 80 de 67 ff 48 89
RSP: 0018:ff11000009a07b60 EFLAGS: 00010286
RAX: 0000000000002bd3 RBX: ff1100000f4e1aa0 RCX: 1ffffffff0e40ac6
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8423ee3c
RBP: ff1100000f4e1af0 R08: 0000000000000001 R09: fffffbfff0e395ae
R10: 0000000000000001 R11: 0000000000036001 R12: ff1100000f4e1af0
R13: dead000000000100 R14: ff1100000f4e1af0 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ff1100006ce80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9b2464bd98 CR3: 0000000005286005 CR4: 0000000000771ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 <TASK>
 ? __warn (kernel/panic.c:748)
 ? ref_tracker_dir_exit (lib/ref_tracker.c:179)
 ? report_bug (lib/bug.c:201 lib/bug.c:219)
 ? handle_bug (arch/x86/kernel/traps.c:285)
 ? exc_invalid_op (arch/x86/kernel/traps.c:309 (discriminator 1))
 ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621)
 ? _raw_spin_unlock_irqrestore (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/spinlock_api_smp.h:151 kernel/locking/spinlock.c:194)
 ? ref_tracker_dir_exit (lib/ref_tracker.c:179)
 ? __pfx_ref_tracker_dir_exit (lib/ref_tracker.c:158)
 ? kfree (mm/slub.c:4613 mm/slub.c:4761)
 net_free (net/core/net_namespace.c:476 net/core/net_namespace.c:467)
 cleanup_net (net/core/net_namespace.c:664 (discriminator 3))
 process_one_work (kernel/workqueue.c:3229)
 worker_thread (kernel/workqueue.c:3304 kernel/workqueue.c:3391
---truncated---

## Which versions are affected by CVE-2025-21678?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21678?

Apply the vendor's patch.

## Is CVE-2025-21678 being exploited?

There is no known exploitation of CVE-2025-21678 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-2025-21678 and fix it if it is affected.

What it is: CVE-2025-21678 is a high-severity use after free vulnerability in Linux kernel, published on 31 Jan 2025. 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-2025-21678 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-2025-21678/ (Markdown: https://insights.sbomify.com/CVE-2025-21678/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21678
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21678
- OSV: https://osv.dev/vulnerability/CVE-2025-21678

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21678/
Summaries are generated and may contain mistakes; the official description above is the record.