netfilter: ctnetlink: fix use-after-free in ctnetlink_dump_exp_ct()

{
  "id": "aae86e38b84e0b275a40ec1a71819aa47797647540ebbcc6121b206098fe929e",
  "url": "https://osv.dev/vulnerability/CVE-2026-23458",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "netfilter: ctnetlink: fix use-after-free in ctnetlink_dump_exp_ct()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: fix use-after-free in ctnetlink_dump_exp_ct() ctnetlink_dump_exp_ct() stores a conntrack pointer in cb->data for the netlink dump callback ctnetlink_exp_ct_dump_table(), but drops the conntrack reference immediately after netlink_dump_start(). When the dump spans multiple rounds, the second recvmsg() triggers the dump callback which dereferences the now-freed conntrack via nfct_help(ct), leading to a use-after-free on ct->ext. The bug is that the netlink_dump_control has no .start or .done callbacks to manage the conntrack reference across dump rounds. Other dump functions in the same file (e.g. ctnetlink_get_conntrack) properly use .start/.done callbacks for this purpose. Fix this by adding .start and .done callbacks that hold and release the conntrack reference for the duration of the dump, and move the nfct_help() call after the cb->args[0] early-return check in the dump callback to avoid dereferencing ct->ext unnecessarily. BUG: KASAN: slab-use-after-free in ctnetlink_exp_ct_dump_table+0x4f/0x2e0 Read of size 8 at addr ffff88810597ebf0 by task ctnetlink_poc/133 CPU: 1 UID: 0 PID: 133 Comm: ctnetlink_poc Not tainted 7.0.0-rc2+ #3 PREEMPTLAZY Call Trace: ctnetlink_exp_ct_dump_table+0x4f/0x2e0 netlink_dump+0x333/0x880 netlink_recvmsg+0x3e2/0x4b0 ? aa_sk_perm+0x184/0x450 sock_recvmsg+0xde/0xf0 Allocated by task 133: kmem_cache_alloc_noprof+0x134/0x440 __nf_conntrack_alloc+0xa8/0x2b0 ctne",
    "evidence": "osv:CVE-2026-23458",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
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        "prerequisites": [],
        "fixed_versions": [
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    "severity": "high",
    "structured": {
      "id": "CVE-2026-23458",
      "aliases": [
        "CVE-2026-23458"
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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": "2026-10-28T02:30:40.928653348Z",
      "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/04c8907ce4e3d3e26c5e1a3e47aa5d17082cbb56",
        "https://git.kernel.org/stable/c/5cb81eeda909dbb2def209dd10636b51549a3f8a",
        "https://git.kernel.org/stable/c/9821b47f669eb82791fa0b1a6ebaf9aa219bea72",
        "https://git.kernel.org/stable/c/bdf2724eefd4455a66863abb025bab8d3aa98c57",
        "https://git.kernel.org/stable/c/cd541f15b60e2257441398cf495d978f816d09f8",
        "https://git.kernel.org/stable/c/d8cd0efbccc5cfb0a80da744a7da76e1333ab925",
        "https://git.kernel.org/stable/c/f025171feef2ac65663d7986f1d5ff0c28d6b2a9",
        "https://git.kernel.org/stable/c/f04cc86d59906513d2d62183b882966fc0ae0390",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23458.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23458",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23458.json"
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        "value": "CVE-2026-23458",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 508717,
  "published_at": "2026-04-03T15:15:39.041+00:00"
}