ipv6: ndisc: fix NULL deref in accept_untracked_na()

{
  "id": "2b70d474195bc97bea2ab2694af398af9d524b5cca67d7e5b66f71a104927f54",
  "url": "https://osv.dev/vulnerability/CVE-2026-64542",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ipv6: ndisc: fix NULL deref in accept_untracked_na()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ipv6: ndisc: fix NULL deref in accept_untracked_na() accept_untracked_na() re-fetches the inet6_dev with __in6_dev_get(dev) and dereferences idev->cnf.accept_untracked_na without a NULL check, even though its only caller ndisc_recv_na() already fetched and NULL-checked idev for the same device. Both reads of dev->ip6_ptr run in the same RCU read-side critical section, but a concurrent addrconf_ifdown() can clear dev->ip6_ptr between them: lowering the MTU below IPV6_MIN_MTU calls addrconf_ifdown() without the synchronize_net() that orders the unregister path, so the re-fetch returns NULL and oopses: BUG: KASAN: null-ptr-deref in ndisc_recv_na (net/ipv6/ndisc.c:974) Read of size 4 at addr 0000000000000364 Call Trace: ndisc_recv_na (net/ipv6/ndisc.c:974) icmpv6_rcv (net/ipv6/icmp.c:1193) ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:479) ip6_input_finish (net/ipv6/ip6_input.c:534) ip6_input (net/ipv6/ip6_input.c:545) ip6_mc_input (net/ipv6/ip6_input.c:635) ipv6_rcv (net/ipv6/ip6_input.c:351) It is reachable by an unprivileged user via a network namespace. Pass the caller's already validated idev instead of re-fetching it; the idev stays alive for the whole RCU critical section, so it is safe even after dev->ip6_ptr has been cleared.",
    "evidence": "osv:CVE-2026-64542",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.183",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.148",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.97",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.40",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.5",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-64542",
      "aliases": [
        "CVE-2026-64542"
      ],
      "affected": [
        {
          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "fixed": "e5ba3017e46f275ad347e762e8eecacec5efa41d"
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                {
                  "fixed": "160d3f0d7a556ceae505dcab521a37057b4ce28f"
                },
                {
                  "fixed": "62c719203cb521b64fab74da94a81bdde5c18808"
                },
                {
                  "fixed": "a6450f7cfae57b382cbaf66a577765c9a88b3c58"
                },
                {
                  "fixed": "63d1c23764de2309cedbb779c75188d257a09d9b"
                },
                {
                  "fixed": "d186e942365acece7c56d39da05dd63bf95b280a"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64542.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.0.0"
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            {
              "type": "ECOSYSTEM",
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                  "introduced": "6.2.0"
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                {
                  "fixed": "6.6.148"
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            },
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.7.0"
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                {
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            {
              "type": "ECOSYSTEM",
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            {
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              "events": [
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                  "introduced": "6.19.0"
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64542.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:42.829763990Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/160d3f0d7a556ceae505dcab521a37057b4ce28f",
        "https://git.kernel.org/stable/c/62c719203cb521b64fab74da94a81bdde5c18808",
        "https://git.kernel.org/stable/c/63d1c23764de2309cedbb779c75188d257a09d9b",
        "https://git.kernel.org/stable/c/a6450f7cfae57b382cbaf66a577765c9a88b3c58",
        "https://git.kernel.org/stable/c/d186e942365acece7c56d39da05dd63bf95b280a",
        "https://git.kernel.org/stable/c/e5ba3017e46f275ad347e762e8eecacec5efa41d",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64542.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-64542",
        "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/2026/64xxx/CVE-2026-64542.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-64542",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 510290,
  "published_at": "2026-07-27T20:10:34.994+00:00"
}