netfilter: nft_ct: fix use-after-free in timeout object destroy

{
  "id": "f6c1deab61a34730d67fe73b134bac721502160d3479d6bbbd34e8b999f4d8ae",
  "url": "https://osv.dev/vulnerability/CVE-2026-31665",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netfilter: nft_ct: fix use-after-free in timeout object destroy",
    "summary": "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",
    "evidence": "osv:CVE-2026-31665",
    "products": [
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          "value": "Kernel",
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        "prerequisites": [],
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    "severity": "high",
    "structured": {
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      "aliases": [
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
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      "modified": "2026-10-28T02:30:37.979935007Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "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/c458fc1c278a65ad5381083121d39a479973ebed",
        "https://git.kernel.org/stable/c/c581e5c8f2b59158f62efe61c1a3dc36189081ff",
        "https://git.kernel.org/stable/c/d0983b48c10d1509fd795c155f8b1e832e1369ff",
        "https://git.kernel.org/stable/c/f16fe84879a5280f05ebbcea593a189ba0f3e79a",
        "https://git.kernel.org/stable/c/f8dca15a1b190787bbd03285304b569631160eda",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31665.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31665",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31665.json"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 505420,
  "published_at": "2026-04-24T14:45:14.613+00:00"
}